Computational metrology

ABSTRACT

A method, involving determining a first distribution of a first parameter associated with an error or residual in performing a device manufacturing process; determining a second distribution of a second parameter associated with an error or residual in performing the device manufacturing process; and determining a distribution of a parameter of interest associated with the device manufacturing process using a function operating on the first and second distributions. The function may include a correlation.

This application is a continuation of co-pending U.S. patent applicationSer. No. 17/197,167, filed Mar. 10, 2021, now allowed, which is acontinuation of U.S. patent application Ser. No. 16/481,143, filed Jul.26, 2019, now U.S. Pat. No. 10,990,018, which is the U.S. national phaseentry of PCT Patent Application No. PCT/EP2018/053412, which was filedon Feb 12, 2018, which claims the benefit of priority of U.S.Provisional Patent Application No. 62/462,201, which was filed on Feb.22, 2017, and of U.S. Provisional Patent Application No. 62/545,578,which was filed on Aug. 15, 2017, each of the foregoing applications isincorporated herein in its entirety by reference.

FIELD

The present disclosure relates to techniques of improving theperformance of a device manufacturing process. The techniques may beused in connection with a lithographic apparatus or a metrologyapparatus.

BACKGROUND

A lithography apparatus is a machine that applies a desired pattern ontoa target portion of a substrate. Lithography apparatus can be used, forexample, in the manufacture of integrated circuits (ICs). In thatcircumstance, a patterning device, which is alternatively referred to asa mask or a reticle, may be used to generate a circuit patterncorresponding to an individual layer of the IC, and this pattern can beimaged onto a target portion (e.g. comprising part of, one or severaldies) on a substrate (e.g. a silicon wafer) that has a layer ofradiation-sensitive material (resist). In general, a single substratewill contain a network of adjacent target portions that are successivelyexposed. Known lithography apparatus include so-called steppers, inwhich each target portion is irradiated by exposing an entire patternonto the target portion in one go, and so-called scanners, in which eachtarget portion is irradiated by scanning the pattern through the beam ina given direction (the “scanning”-direction) while synchronouslyscanning the substrate parallel or anti parallel to this direction.

Prior to transferring the circuit pattern from the patterning device tothe substrate, the substrate may undergo various procedures, such aspriming, resist coating and a soft bake. After exposure, the substratemay be subjected to other procedures, such as a post-exposure bake(PEB), development, a hard bake and measurement/inspection of thetransferred circuit pattern. This array of procedures is used as a basisto make an individual layer of a device, e.g., an IC. The substrate maythen undergo various processes such as etching, ion-implantation(doping), metallization, oxidation, chemo-mechanical polishing, etc.,all intended to finish off the individual layer of the device. Ifseveral layers are required in the device, then the whole procedure, ora variant thereof, is repeated for each layer. Eventually, a device willbe present in each target portion on the substrate. These devices arethen separated from one another by a technique such as dicing or sawing,whence the individual devices can be mounted on a carrier, connected topins, etc.

Thus, manufacturing devices, such as semiconductor devices, typicallyinvolves processing a substrate (e.g., a semiconductor wafer) using anumber of fabrication processes to form various features and multiplelayers of the devices. Such layers and features are typicallymanufactured and processed using, e.g., deposition, lithography, etch,chemical-mechanical polishing, and ion implantation. Multiple devicesmay be fabricated on a plurality of dies on a substrate and thenseparated into individual devices. This device manufacturing process maybe considered a patterning process. A patterning process involves apatterning step, such as optical and/or nanoimprint lithography using apatterning device in a lithographic apparatus, to transfer a pattern onthe patterning device to a substrate and typically, but optionally,involves one or more related pattern processing steps, such as resistdevelopment by a development apparatus, baking of the substrate using abake tool, etching using the pattern using an etch apparatus, etc.

SUMMARY

In an embodiment, there is disclose a method comprising: determining afirst distribution of a first parameter associated with an error orresidual in performing a device manufacturing process; determining asecond distribution of a second parameter associated with an error orresidual in performing the device manufacturing process; anddetermining, by a hardware computer, a distribution of a parameter ofinterest associated with the device manufacturing process using afunction operating on the first and second distributions.

In an embodiment, there is provided a method comprising: obtaining anunderlying contribution of a lithographic apparatus to overlay as partof a patterning process; and combining, by a hardware computer, theunderlying contribution with a further contribution to overlay of asubstrate to obtain an estimate of overlay for the substrate.

In an embodiment, there is provided a method, comprising: determining afirst distribution of measured alignment data in performing a devicemanufacturing process; determining a second distribution of alignmentdata derived from a processing parameter in the device manufacturingprocess; and determining, by a hardware computer system, a distributionof alignment data associated with the device manufacturing process as afunction of the first and second distributions.

In an embodiment, there is provided a method comprising: obtaining analignment data distribution across at least part of a substrateprocessed using a patterning process, based on measured alignment data;and combining, by a hardware computer, the alignment data distributionwith an alignment fingerprint attributable to a processing parameterother than measured alignment to obtain an estimate of alignment datafor the substrate.

In an embodiment, there is provided a computer program productcomprising a non-transitory computer readable medium having instructionsrecorded thereon, the instructions when executed by a computerimplementing any of the methods herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a lithography apparatus according to anembodiment.

FIG. 2 schematically depicts an embodiment of a lithographic cell orcluster;

FIG. 3 schematically depicts an example inspection apparatus andmetrology technique.

FIG. 4 schematically depicts an example inspection apparatus.

FIG. 5 illustrates the relationship between an illumination spot of aninspection apparatus and a metrology target.

FIG. 6 schematically depicts a process of deriving a plurality ofvariables of interest based on measurement data.

FIG. 7 shows example categories of processing variables.

FIG. 8 schematically shows that changes of processing variables may havecontributions to metrology data.

FIG. 9 schematically shows an example of deriving a combinedcontribution to a patterning process parameter.

FIG. 10 schematically shows an example of deriving a contribution to aprocessing variable from metrology data.

FIG. 11 schematically shows a flow for a method, according to anembodiment.

FIG. 12 schematically shows a flow for a method, according to anembodiment.

FIG. 13 schematically shows a flow for a method, according to anembodiment.

FIG. 14 schematically depicts an example contribution/fingerprint and anembodiment of selection of a contour.

FIG. 15 schematically depicts an example contribution/fingerprint and anembodiment of modification of a contour.

FIGS. 16A, 16B and 16C schematically depict an embodiment of a defectanalysis process.

FIGS. 17A, 17B and 17C schematically depict an embodiment of a defectanalysis process.

FIG. 18 schematically shows an example of deriving a combinedcontribution for alignment.

FIG. 19 schematically shows an example of deriving a combinedcontribution for alignment.

FIG. 20 schematically shows an example of how a patterning processcorrected using a fingerprint determined according to an existingalignment measurement scheme translates to an overlay error fingerprint.

FIG. 21 schematically shows an example of how a patterning processcorrected using a derived fingerprint of alignment computed as describedherein translates to overlay error.

FIG. 22 schematically shows a flow for a method, according to anembodiment.

FIGS. 23 and 24 schematically show adjusting calibration factors topredict distribution.

FIG. 25 schematically shows the determination of the possibility ofcorrect prediction.

FIG. 26 is a block diagram of an example computer system.

DETAILED DESCRIPTION

Before describing embodiments in detail, it is instructive to present anexample environment in which embodiments may be implemented.

FIG. 1 schematically depicts an embodiment of a lithographic apparatusLA. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT (e.g., WTa, WTb or both)constructed to hold a substrate (e.g. a resist-coated wafer) W andconnected to a second positioner PW configured to accurately positionthe substrate in accordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies and often referred to as fields) of the substrate W, theprojection system supported on a reference frame (RF).

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The illuminator IL receives a beam of radiation from a radiation sourceSO. The source and the lithographic apparatus may be separate entities,for example when the source is an excimer laser. In such cases, thesource is not considered to form part of the lithographic apparatus andthe radiation beam is passed from the source SO to the illuminator ILwith the aid of a beam delivery system BD comprising for examplesuitable directing mirrors and/or a beam expander. In other cases thesource may be an integral part of the apparatus, for example when thesource is a mercury lamp. The source SO and the illuminator IL, togetherwith the beam delivery system BD if required, may be referred to as aradiation system.

The illuminator IL may alter the intensity distribution of the beam. Theilluminator may be arranged to limit the radial extent of the radiationbeam such that the intensity distribution is non-zero within an annularregion in a pupil plane of the illuminator IL. Additionally oralternatively, the illuminator IL may be operable to limit thedistribution of the beam in the pupil plane such that the intensitydistribution is non-zero in a plurality of equally spaced sectors in thepupil plane. The intensity distribution of the radiation beam in a pupilplane of the illuminator IL may be referred to as an illumination mode.

So, the illuminator IL may comprise adjuster AM configured to adjust the(angular/spatial) intensity distribution of the beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. The illuminator IL maybe operable to vary the angular distribution of the beam. For example,the illuminator may be operable to alter the number, and angular extent,of sectors in the pupil plane wherein the intensity distribution isnon-zero. By adjusting the intensity distribution of the beam in thepupil plane of the illuminator, different illumination modes may beachieved. For example, by limiting the radial and angular extent of theintensity distribution in the pupil plane of the illuminator IL, theintensity distribution may have a multi-pole distribution such as, forexample, a dipole, quadrupole or hexapole distribution. A desiredillumination mode may be obtained, e.g., by inserting an optic whichprovides that illumination mode into the illuminator IL or using aspatial light modulator.

The illuminator IL may be operable alter the polarization of the beamand may be operable to adjust the polarization using adjuster AM. Thepolarization state of the radiation beam across a pupil plane of theilluminator IL may be referred to as a polarization mode. The use ofdifferent polarization modes may allow greater contrast to be achievedin the image formed on the substrate W. The radiation beam may beunpolarized. Alternatively, the illuminator may be arranged to linearlypolarize the radiation beam. The polarization direction of the radiationbeam may vary across a pupil plane of the illuminator IL. Thepolarization direction of radiation may be different in differentregions in the pupil plane of the illuminator IL. The polarization stateof the radiation may be chosen in dependence on the illumination mode.For multi-pole illumination modes, the polarization of each pole of theradiation beam may be generally perpendicular to the position vector ofthat pole in the pupil plane of the illuminator IL. For example, for adipole illumination mode, the radiation may be linearly polarized in adirection that is substantially perpendicular to a line that bisects thetwo opposing sectors of the dipole. The radiation beam may be polarizedin one of two different orthogonal directions, which may be referred toas X-polarized and Y-polarized states. For a quadrupole illuminationmode the radiation in the sector of each pole may be linearly polarizedin a direction that is substantially perpendicular to a line thatbisects that sector. This polarization mode may be referred to as XYpolarization. Similarly, for a hexapole illumination mode the radiationin the sector of each pole may be linearly polarized in a direction thatis substantially perpendicular to a line that bisects that sector. Thispolarization mode may be referred to as TE polarization.

In addition, the illuminator IL generally comprises various othercomponents, such as an integrator IN and a condenser CO. Theillumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

Thus, the illuminator provides a conditioned beam of radiation B, havinga desired uniformity and intensity distribution in its cross section.

The support structure MT supports the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a pattern in atarget portion of the substrate. In an embodiment, a patterning deviceis any device that can be used to impart a radiation beam with a patternin its cross-section so as to create a pattern in a target portion ofthe substrate. It should be noted that the pattern imparted to theradiation beam may not exactly correspond to the desired pattern in thetarget portion of the substrate, for example if the pattern includesphase-shifting features or so called assist features. Generally, thepattern imparted to the radiation beam will correspond to a particularfunctional layer in a device being created in the target portion, suchas an integrated circuit.

A patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam, which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

The projection system PS has an optical transfer function which may benon-uniform, which can affect the pattern imaged on the substrate W. Forunpolarized radiation such effects can be fairly well described by twoscalar maps, which describe the transmission (apodization) and relativephase (aberration) of radiation exiting the projection system PS as afunction of position in a pupil plane thereof. These scalar maps, whichmay be referred to as the transmission map and the relative phase map,may be expressed as a linear combination of a complete set of basisfunctions. A particularly convenient set is the Zernike polynomials,which form a set of orthogonal polynomials defined on a unit circle. Adetermination of each scalar map may involve determining thecoefficients in such an expansion. Since the Zernike polynomials areorthogonal on the unit circle, the Zernike coefficients may bedetermined by calculating the inner product of a measured scalar mapwith each Zernike polynomial in turn and dividing this by the square ofthe norm of that Zernike polynomial.

The transmission map and the relative phase map are field and systemdependent. That is, in general, each projection system PS will have adifferent Zernike expansion for each field point (i.e. for each spatiallocation in its image plane). The relative phase of the projectionsystem PS in its pupil plane may be determined by projecting radiation,for example from a point-like source in an object plane of theprojection system PS (i.e. the plane of the patterning device MA),through the projection system PS and using a shearing interferometer tomeasure a wavefront (i.e. a locus of points with the same phase). Ashearing interferometer is a common path interferometer and therefore,advantageously, no secondary reference beam is required to measure thewavefront. The shearing interferometer may comprise a diffractiongrating, for example a two dimensional grid, in an image plane of theprojection system (i.e. the substrate table WT) and a detector arrangedto detect an interference pattern in a plane that is conjugate to apupil plane of the projection system PS. The interference pattern isrelated to the derivative of the phase of the radiation with respect toa coordinate in the pupil plane in the shearing direction. The detectormay comprise an array of sensing elements such as, for example, chargecoupled devices (CCDs).

The projection system PS of a lithography apparatus may not producevisible fringes and therefore the accuracy of the determination of thewavefront can be enhanced using phase stepping techniques such as, forexample, moving the diffraction grating. Stepping may be performed inthe plane of the diffraction grating and in a direction perpendicular tothe scanning direction of the measurement. The stepping range may be onegrating period, and at least three (uniformly distributed) phase stepsmay be used. Thus, for example, three scanning measurements may beperformed in the y-direction, each scanning measurement being performedfor a different position in the x-direction. This stepping of thediffraction grating effectively transforms phase variations intointensity variations, allowing phase information to be determined. Thegrating may be stepped in a direction perpendicular to the diffractiongrating (z direction) to calibrate the detector.

The diffraction grating may be sequentially scanned in two perpendiculardirections, which may coincide with axes of a co-ordinate system of theprojection system PS (x and y) or may be at an angle such as 45 degreesto these axes. Scanning may be performed over an integer number ofgrating periods, for example one grating period. The scanning averagesout phase variation in one direction, allowing phase variation in theother direction to be reconstructed. This allows the wavefront to bedetermined as a function of both directions.

The transmission (apodization) of the projection system PS in its pupilplane may be determined by projecting radiation, for example from apoint-like source in an object plane of the projection system PS (i.e.the plane of the patterning device MA), through the projection system PSand measuring the intensity of radiation in a plane that is conjugate toa pupil plane of the projection system PS, using a detector. The samedetector as is used to measure the wavefront to determine aberrationsmay be used.

The projection system PS may comprise a plurality of optical (e.g.,lens) elements and may further comprise an adjustment mechanism AMconfigured to adjust one or more of the optical elements so as tocorrect for aberrations (phase variations across the pupil planethroughout the field). To achieve this, the adjustment mechanism may beoperable to manipulate one or more optical (e.g., lens) elements withinthe projection system PS in one or more different ways. The projectionsystem may have a co-ordinate system wherein its optical axis extends inthe z direction. The adjustment mechanism may be operable to do anycombination of the following: displace one or more optical elements;tilt one or more optical elements; and/or deform one or more opticalelements. Displacement of an optical element may be in any direction (x,y, z or a combination thereof). Tilting of an optical element istypically out of a plane perpendicular to the optical axis, by rotatingabout an axis in the x and/or y directions although a rotation about thez axis may be used for a non-rotationally symmetric aspherical opticalelement. Deformation of an optical element may include a low frequencyshape (e.g. astigmatic) and/or a high frequency shape (e.g. free formaspheres). Deformation of an optical element may be performed forexample by using one or more actuators to exert force on one or moresides of the optical element and/or by using one or more heatingelements to heat one or more selected regions of the optical element. Ingeneral, it may not be possible to adjust the projection system PS tocorrect for apodization (transmission variation across the pupil plane).The transmission map of a projection system PS may be used whendesigning a patterning device (e.g., mask) MA for the lithographyapparatus LA. Using a computational lithography technique, thepatterning device MA may be designed to at least partially correct forapodization.

The lithographic apparatus may be of a type having two (dual stage) ormore tables (e.g., two or more substrate tables WTa, WTb, two or morepatterning device tables, a substrate table WTa and a table WTb belowthe projection system without a substrate that is dedicated to, forexample, facilitating measurement, and/or cleaning, etc.). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure. For example, alignmentmeasurements using an alignment sensor AS and/or level (height, tilt,etc.) measurements using a level sensor LS may be made.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the patterning device and the projection system. Immersiontechniques are well known in the art for increasing the numericalaperture of projection systems. The term “immersion” as used herein doesnot mean that a structure, such as a substrate, must be submerged inliquid, but rather only means that liquid is located between theprojection system and the substrate during exposure.

So, in operation of the lithographic apparatus, a radiation beam isconditioned and provided by the illumination system IL. The radiationbeam B is incident on the patterning device (e.g., mask) MA, which isheld on the support structure (e.g., mask table) MT, and is patterned bythe patterning device. Having traversed the patterning device MA, theradiation beam B passes through the projection system PS, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g. an interferometricdevice, linear encoder, 2-D encoder or capacitive sensor), the substratetable WT can be moved accurately, e.g. so as to position differenttarget portions C in the path of the radiation beam B. Similarly, thefirst positioner PM and another position sensor (which is not explicitlydepicted in FIG. 1) can be used to accurately position the patterningdevice MA with respect to the path of the radiation beam B, e.g. aftermechanical retrieval from a mask library, or during a scan. In general,movement of the support structure MT may be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the first positioner PM. Similarly,movement of the substrate table WT may be realized using a long-strokemodule and a short-stroke module, which form part of the secondpositioner PW. In the case of a stepper (as opposed to a scanner) thesupport structure MT may be connected to a short-stroke actuator only,or may be fixed. Patterning device MA and substrate W may be alignedusing patterning device alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on thepatterning device MA, the patterning device alignment marks may belocated between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Although specific reference may be made in this text to the use oflithography apparatus in the manufacture of ICs, it should be understoodthat the lithography apparatus described herein may have otherapplications, such as the manufacture of integrated optical systems,guidance and detection patterns for magnetic domain memories,liquid-crystal displays (LCDs), thin film magnetic heads, etc. Theskilled artisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” herein may beconsidered as synonymous with the more general terms “substrate” or“target portion”, respectively. The substrate referred to herein may beprocessed, before or after exposure, in for example a track (a tool thattypically applies a layer of resist to a substrate and develops theexposed resist) or a metrology or inspection tool. Where applicable, thedisclosure herein may be applied to such and other substrate processingtools. Further, the substrate may be processed more than once, forexample in order to create a multi-layer IC, so that the term substrateused herein may also refer to a substrate that already contains multipleprocessed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of 365, 248, 193, 157 or 126 nm) and extremeultra-violet (EUV) radiation (e.g. having a wavelength in the range of5-20 nm), as well as particle beams, such as ion beams or electronbeams.

Various patterns on or provided by a patterning device may havedifferent process windows. i.e., a space of processing variables underwhich a pattern will be produced within specification. Examples ofpattern specifications that relate to potential systematic defectsinclude checks for necking, line pull back, line thinning, CD, edgeplacement, overlapping, resist top loss, resist undercut and/orbridging. The process window of all the patterns on a patterning deviceor an area thereof may be obtained by merging (e.g., overlapping)process windows of each individual pattern. The boundary of the processwindow of all the patterns contains boundaries of process windows ofsome of the individual patterns. In other words, these individualpatterns limit the process window of all the patterns. These patternscan be referred to as “hot spots” or “process window limiting patterns(PWLPs),” which are used interchangeably herein. When controlling apatterning process, it is possible and economical to focus on the hotspots. When the hot spots are not defective, it is most likely that allthe patterns are not defective.

As shown in FIG. 2, the lithographic apparatus LA may form part of alithographic cell LC, also sometimes referred to a lithocell or cluster,which also includes apparatuses to perform pre- and post-exposureprocesses on a substrate. Conventionally these include one or more spincoaters SC to deposit one or more resist layers, one or more developersDE to develop exposed resist, one or more chill plates CH and/or one ormore bake plates BK. A substrate handler, or robot, RO picks up one ormore substrates from input/output port I/O1, I/O2, moves them betweenthe different process apparatuses and delivers them to the loading bayLB of the lithographic apparatus. These apparatuses, which are oftencollectively referred to as the track, are under the control of a trackcontrol unit TCU which is itself controlled by the supervisory controlsystem SCS, which also controls the lithographic apparatus vialithography control unit LACU. Thus, the different apparatuses can beoperated to maximize throughput and processing efficiency.

In order that a substrate that is exposed by the lithographic apparatusis exposed correctly and consistently and/or in order to monitor thepatterning process (e.g., a device manufacturing process) that includesat least one pattern transfer step (e.g., an optical lithography step),it is desirable to inspect a substrate or other object to measure ordetermine one or more properties such as alignment, overlay (which canbe, for example, between structures in overlying layers or betweenstructures in a same layer that have been provided separately to thelayer by, for example, a double patterning process), line thickness,critical dimension (CD), focus offset, a material property, etc.Accordingly a manufacturing facility in which lithocell LC is locatedalso typically includes a metrology system MET which measures some orall of the substrates W that have been processed in the lithocell orother objects in the lithocell. The metrology system MET may be part ofthe lithocell LC, for example it may be part of the lithographicapparatus LA (such as alignment sensor AS).

The one or more measured parameters may include, for example, overlaybetween successive layers formed in or on the patterned substrate,critical dimension (CD) (e.g., critical linewidth) of, for example,features formed in or on the patterned substrate, focus or focus errorof an optical lithography step, dose or dose error of an opticallithography step, optical aberrations of an optical lithography step,etc. This measurement may be performed on a target of the productsubstrate itself and/or on a dedicated metrology target provided on thesubstrate. The measurement can be performed after-development of aresist but before etching or can be performed after-etch.

There are various techniques for making measurements of the structuresformed in the patterning process, including the use of a scanningelectron microscope, an image-based measurement tool and/or variousspecialized tools. As discussed above, a fast and non-invasive form ofspecialized metrology tool is one in which a beam of radiation isdirected onto a target on the surface of the substrate and properties ofthe scattered (diffracted/reflected) beam are measured. By evaluatingone or more properties of the radiation scattered by the substrate, oneor more properties of the substrate can be determined. This may betermed diffraction-based metrology. One such application of thisdiffraction-based metrology is in the measurement of feature asymmetrywithin a target. This can be used as a measure of overlay, for example,but other applications are also known. For example, asymmetry can bemeasured by comparing opposite parts of the diffraction spectrum (forexample, comparing the −1st and +1^(st) orders in the diffractionspectrum of a periodic grating). This can be done as described above andas described, for example, in U.S. patent application publication US2006-066855, which is incorporated herein in its entirety by reference.Another application of diffraction-based metrology is in the measurementof feature width (CD) within a target. Such techniques can use theapparatus and methods described hereafter.

Thus, in a device fabrication process (e.g., a patterning process or alithography process), a substrate or other objects may be subjected tovarious types of measurement during or after the process. Themeasurement may determine whether a particular substrate is defective,may establish adjustments to the process and apparatuses used in theprocess (e.g., aligning two layers on the substrate or aligning thepatterning device to the substrate), may measure the performance of theprocess and the apparatuses, or may be for other purposes. Examples ofmeasurement include optical imaging (e.g., optical microscope),non-imaging optical measurement (e.g., measurement based on diffractionsuch as ASML YieldStar metrology tool, ASML SMASH metrology system),mechanical measurement (e.g., profiling using a stylus, atomic forcemicroscopy (AFM)), and/or non-optical imaging (e.g., scanning electronmicroscopy (SEM)). The SMASH (SMart Alignment Sensor Hybrid) system, asdescribed in U.S. Pat. No. 6,961,116, which is incorporated by referenceherein in its entirety, employs a self-referencing interferometer thatproduces two overlapping and relatively rotated images of an alignmentmarker, detects intensities in a pupil plane where Fourier transforms ofthe images are caused to interfere, and extracts the positionalinformation from the phase difference between diffraction orders of thetwo images which manifests as intensity variations in the interferedorders.

Metrology results may be provided directly or indirectly to thesupervisory control system SCS. If an error is detected, an adjustmentmay be made to exposure of a subsequent substrate (especially if theinspection can be done soon and fast enough that one or more othersubstrates of the batch are still to be exposed) and/or to subsequentexposure of the exposed substrate. Also, an already exposed substratemay be stripped and reworked to improve yield, or discarded, therebyavoiding performing further processing on a substrate known to befaulty. In a case where only some target portions of a substrate arefaulty, further exposures may be performed only on those target portionswhich are good.

Within a metrology system MET, a metrology apparatus is used todetermine one or more properties of the substrate, and in particular,how one or more properties of different substrates vary or differentlayers of the same substrate vary from layer to layer. As noted above,the metrology apparatus may be integrated into the lithographicapparatus LA or the lithocell LC or may be a stand-alone device.

To enable the metrology, one or more targets can be provided on thesubstrate. In an embodiment, the target is specially designed and maycomprise a periodic structure. In an embodiment, the target is a part ofa device pattern, e.g., a periodic structure of the device pattern. Inan embodiment, the device pattern is a periodic structure of a memorydevice (e.g., a Bipolar Transistor (BPT), a Bit Line Contact (BLC), etc.structure).

In an embodiment, the target on a substrate may comprise one or more 1-Dperiodic structures (e.g., gratings), which are printed such that afterdevelopment, the periodic structural features are formed of solid resistlines. In an embodiment, the target may comprise one or more 2-Dperiodic structures (e.g., gratings), which are printed such that afterdevelopment, the one or more periodic structures are formed of solidresist pillars or vias in the resist. The bars, pillars or vias mayalternatively be etched into the substrate (e.g., into one or morelayers on the substrate).

In an embodiment, one of the parameters of interest of a patterningprocess is overlay. Overlay can be measured using dark fieldscatterometry in which the zeroth order of diffraction (corresponding toa specular reflection) is blocked, and only higher orders processed.Examples of dark field metrology can be found in PCT patent applicationpublication nos. WO 2009/078708 and WO 2009/106279, which are herebyincorporated in their entirety by reference. Further developments of thetechnique have been described in U.S. patent application publicationsUS2011-0027704, US2011-0043791 and US2012-0242970, which are herebyincorporated in their entirety by reference. Diffraction-based overlayusing dark-field detection of the diffraction orders enables overlaymeasurements on smaller targets. These targets can be smaller than theillumination spot and may be surrounded by device product structures ona substrate. In an embodiment, multiple targets can be measured in oneradiation capture.

FIG. 3 depicts an example inspection apparatus (e.g., a scatterometer).It comprises a broadband (white light) radiation projector 2 whichprojects radiation onto a substrate W. The redirected radiation ispassed to a spectrometer detector 4, which measures a spectrum 10(intensity as a function of wavelength) of the specular reflectedradiation, as shown, e.g., in the graph in the lower left. From thisdata, the structure or profile giving rise to the detected spectrum maybe reconstructed by processor PU, e.g. by Rigorous Coupled Wave Analysisand non-linear regression or by comparison with a library of simulatedspectra as shown at the bottom right of FIG. 3. In general, for thereconstruction the general form of the structure is known and somevariables are assumed from knowledge of the process by which thestructure was made, leaving only a few variables of the structure to bedetermined from the measured data. Such an inspection apparatus may beconfigured as a normal-incidence inspection apparatus or anoblique-incidence inspection apparatus.

Another inspection apparatus that may be used is shown in FIG. 4. Inthis device, the radiation emitted by radiation source 2 is collimatedusing lens system 12 and transmitted through interference filter 13 andpolarizer 17, reflected by partially reflecting surface 16 and isfocused into a spot S on substrate W via an objective lens 15, which hasa high numerical aperture (NA), desirably at least 0.9 or at least 0.95.An immersion inspection apparatus (using a relatively high refractiveindex fluid such as water) may even have a numerical aperture over 1.

As in the lithographic apparatus LA, one or more substrate tables may beprovided to hold the substrate W during measurement operations. Thesubstrate tables may be similar or identical in form to the substratetable WT of FIG. 1. In an example where the inspection apparatus isintegrated with the lithographic apparatus, they may even be the samesubstrate table. Coarse and fine positioners may be provided to a secondpositioner PW configured to accurately position the substrate inrelation to a measurement optical system. Various sensors and actuatorsare provided for example to acquire the position of a target ofinterest, and to bring it into position under the objective lens 15.Typically many measurements will be made on targets at differentlocations across the substrate W. The substrate support can be moved inX and Y directions to acquire different targets, and in the Z directionto obtain a desired location of the target relative to the focus of theoptical system. It is convenient to think and describe operations as ifthe objective lens is being brought to different locations relative tothe substrate, when, for example, in practice the optical system mayremain substantially stationary (typically in the X and Y directions,but perhaps also in the Z direction) and only the substrate moves.Provided the relative position of the substrate and the optical systemis correct, it does not matter in principle which one of those is movingin the real world, or if both are moving, or a combination of a part ofthe optical system is moving (e.g., in the Z and/or tilt direction) withthe remainder of the optical system being stationary and the substrateis moving (e.g., in the X and Y directions, but also optionally in the Zand/or tilt direction).

The radiation redirected by the substrate W then passes throughpartially reflecting surface 16 into a detector 18 in order to have thespectrum detected. The detector 18 may be located at a back-projectedfocal plane 11 (i.e., at the focal length of the lens system 15) or theplane 11 may be re-imaged with auxiliary optics (not shown) onto thedetector 18. The detector may be a two-dimensional detector so that atwo-dimensional angular scatter spectrum of a substrate target 30 can bemeasured. The detector 18 may be, for example, an array of CCD or CMOSsensors, and may use an integration time of, for example, 40milliseconds per frame.

A reference beam may be used, for example, to measure the intensity ofthe incident radiation. To do this, when the radiation beam is incidenton the partially reflecting surface 16 part of it is transmitted throughthe partially reflecting surface 16 as a reference beam towards areference mirror 14. The reference beam is then projected onto adifferent part of the same detector 18 or alternatively on to adifferent detector (not shown).

One or more interference filters 13 are available to select a wavelengthof interest in the range of, say, 405-790 nm or even lower, such as200-300 nm. The interference filter may be tunable rather thancomprising a set of different filters. A grating could be used insteadof an interference filter. An aperture stop or spatial light modulator(not shown) may be provided in the illumination path to control therange of angle of incidence of radiation on the target.

The detector 18 may measure the intensity of redirected radiation at asingle wavelength (or narrow wavelength range), the intensity separatelyat multiple wavelengths or integrated over a wavelength range.Furthermore, the detector may separately measure the intensity oftransverse magnetic- and transverse electric-polarized radiation and/orthe phase difference between the transverse magnetic- and transverseelectric-polarized radiation.

The target 30 on substrate W may be a 1-D grating, which is printed suchthat after development, the bars are formed of solid resist lines. Thetarget 30 may be a 2-D grating, which is printed such that afterdevelopment, the grating is formed of solid resist pillars or vias inthe resist. The bars, pillars or vias may be etched into or on thesubstrate (e.g., into one or more layers on the substrate). The pattern(e.g., of bars, pillars or vias) is sensitive to change in processing inthe patterning process (e.g., optical aberration in the lithographicprojection apparatus (particularly the projection system PS), focuschange, dose change, etc.) and will manifest in a variation in theprinted grating. Accordingly, the measured data of the printed gratingis used to reconstruct the grating. One or more parameters of the 1-Dgrating, such as line width and/or shape, or one or more parameters ofthe 2-D grating, such as pillar or via width or length or shape, may beinput to the reconstruction process, performed by processor PU, fromknowledge of the printing step and/or other inspection processes.

In addition to measurement of a parameter by reconstruction, angleresolved scatterometry is useful in the measurement of asymmetry offeatures in product and/or resist patterns. A particular application ofasymmetry measurement is for the measurement of overlay, where thetarget 30 comprises one set of periodic features superimposed onanother. The concepts of asymmetry measurement using the instrument ofFIG. 3 or FIG. 4 are described, for example, in U.S. patent applicationpublication US2006-066855, which is incorporated herein in its entirety.Simply stated, while the positions of the diffraction orders in thediffraction spectrum of the target are determined only by theperiodicity of the target, asymmetry in the diffraction spectrum isindicative of asymmetry in the individual features which make up thetarget. In the instrument of FIG. 4, where detector 18 may be an imagesensor, such asymmetry in the diffraction orders appears directly asasymmetry in the pupil image recorded by detector 18. This asymmetry canbe measured by digital image processing in unit PU, and calibratedagainst known values of overlay.

FIG. 5 illustrates a plan view of a typical target 30, and the extent ofillumination spot S in the apparatus of FIG. 4. To obtain a diffractionspectrum that is free of interference from surrounding structures, thetarget 30, in an embodiment, is a periodic structure (e.g., grating)larger than the width (e.g., diameter) of the illumination spot S. Thewidth of spot S may be smaller than the width and length of the target.The target in other words is ‘underfilled’ by the illumination, and thediffraction signal is essentially free from any signals from productfeatures and the like outside the target itself. The illuminationarrangement 2, 12, 13, 17 may be configured to provide illumination of auniform intensity across a back focal plane of objective 15.Alternatively, by, e.g., including an aperture in the illumination path,illumination may be restricted to on axis or off axis directions.

FIG. 6 schematically depicts an example process of the determination ofthe value of one or more variables of interest of a target pattern 30′based on measurement data obtained using metrology. Radiation detectedby the detector 18 provides a measured radiation distribution 108 fortarget 30′.

For a given target 30′, a radiation distribution 208 can becomputed/simulated from a parameterized model 206 using, for example, anumerical Maxwell solver 210. The parameterized model 206 shows examplelayers of various materials making up, and associated with, the target.The parameterized model 206 may include one or more of variables for thefeatures and layers of the portion of the target under consideration,which may be varied and derived. As shown in FIG. 6, the one or more ofthe variables may include the thickness t of one or more layers, a widthw (e.g., CD) of one or more features, a height h of one or morefeatures, and/or a sidewall angle a of one or more features. Althoughnot shown, the one or more of the variables may further include, but isnot limited to, the refractive index (e.g., a real or complex refractiveindex, refractive index tensor, etc.) of one or more of the layers, theextinction coefficient of one or more layers, the absorption of one ormore layers, resist loss during development, a footing of one or morefeatures, and/or line edge roughness of one or more features. Theinitial values of the variables may be those expected for the targetbeing measured. The measured radiation distribution 108 is then comparedat 212 to the computed radiation distribution 208 to determine thedifference between the two. If there is a difference, the values of oneor more of the variables of the parameterized model 206 may be varied, anew computed radiation distribution 208 calculated and compared againstthe measured radiation distribution 108 until there is sufficient matchbetween the measured radiation distribution 108 and the computedradiation distribution 208. At that point, the values of the variablesof the parameterized model 206 provide a good or best match of thegeometry of the actual target 30′. In an embodiment, there is sufficientmatch when a difference between the measured radiation distribution 108and the computed radiation distribution 208 is within a tolerancethreshold.

Variables of a patterning process are called “processing variables.” Thepatterning process may include processes upstream and downstream to theactual transfer of the pattern in a lithography apparatus. FIG. 7 showsexample categories of the processing variables 370. The first categorymay be variables 310 of the lithography apparatus or any otherapparatuses used in the lithography process. Examples of this categoryinclude variables of the illumination, projection system, substratestage, etc. of a lithography apparatus. The second category may bevariables 320 of one or more procedures performed in the patterningprocess. Examples of this category include focus control or focusmeasurement, dose control or dose measurement, bandwidth, exposureduration, development temperature, chemical composition used indevelopment, etc. The third category may be variables 330 of the designlayout and its implementation in, or using, a patterning device.Examples of this category may include shapes and/or locations of assistfeatures, adjustments applied by a resolution enhancement technique(RET), CD of mask features, etc. The fourth category may be variables340 of the substrate. Examples include characteristics of structuresunder a resist layer, chemical composition and/or physical dimension ofthe resist layer, etc. The fifth category may be characteristics 350 oftemporal variation of one or more variables of the patterning process.Examples of this category include a characteristic of high frequencystage movement (e.g., frequency, amplitude, etc.), high frequency laserbandwidth change (e.g., frequency, amplitude, etc.) and/or highfrequency laser wavelength change. These high frequency changes ormovements are those above the response time of mechanisms to adjust theunderlying variables (e.g., stage position, laser intensity). The sixthcategory may be characteristics 360 of processes upstream of, ordownstream to, pattern transfer in a lithographic apparatus, such asspin coating, post-exposure bake (PEB), development, etching,deposition, doping and/or packaging.

As will be appreciated, many, if not all of these variables, will havean effect on a parameter of the patterning process and often a parameterof interest. Non-limiting examples of parameters of the patterningprocess may include critical dimension (CD), critical dimensionuniformity (CDU), focus, overlay, edge position or placement, sidewallangle, pattern shift, etc. Often, these parameters express an error froma nominal value (e.g., a design value, an average value, etc.). Theparameter values may be the values of a characteristic of individualpatterns or a statistic (e.g., average, variance, etc.) of thecharacteristic of a group of patterns.

The values of some or all of the processing variables, or a parameterrelated thereto, may be determined by a suitable method. For example,the values may be determined from data obtained with various metrologytools (e.g., a substrate metrology tool). The values may be obtainedfrom various sensors or systems of an apparatus in the patterningprocess (e.g., a sensor, such as a leveling sensor or alignment sensor,of a lithography apparatus, a control system (e.g., a substrate orpatterning device table control system) of a lithography apparatus, asensor in a track tool, etc.). The values may be from an operator of thepatterning process.

Now, increasingly metrology has become a burden mostly in terms of timetaken. This is, for example, particularly the case in the advent ofmultiple patterning techniques in the semiconductor industry. Withmultiple patterning techniques such as litho-etch-litho-etch (LELE)and/or sidewall assisted double patterning (SADP), the number ofprocessing steps has increased significantly and therefore, so has theamount of metrology steps used for control and yield monitoring.Moreover, the amount of metrology increases for each node (i.e.,reduction in feature size) as more layers are used in multiplepatterning steps, and more patterning steps are used per layer.

Additionally or alternatively, there is an increased desire for defectdetermination and/or guided defect inspection. This involvessubstantially denser focus, overlay, and/or CD metrology than before.

Additionally or alternatively, there are ever tightening specificationson on-device CD, overlay, and/or focus performance. This drivesmanufacturing equipment specifications of, e.g., exposure tools andprocessing tools (e.g., deposition, etch, track, chemical mechanicalpolishing (CMP), etc.), from one node to the next. So, this drivestighter control and monitoring of performance which in turn drives thedemand for ever increasing amounts of metrology for control andmonitoring.

Additionally or alternatively, in line with tightening of thespecifications on on-device CD, focus, and/or overlay performance,higher order corrections may be needed. A higher order correction isessentially a corrective action which is selective on a small spatialscale across all or part of the substrate (e.g. correction with a highspatial resolution). Higher order correction involves a denser samplingper substrate for metrology, thereby increasing the metrology burdenperhaps beyond practical limits of metrology equipment productivity.

Additionally or alternatively, substrate to substrate variation mayrequire further individual substrate level control (compared to, e.g.,lot level control) and associated monitoring in order to achieve thedesired CD, focus, and/or overlay performance. This may lead tomeasuring more substrates per lot and thus drive an increase in theamount of measurements used, perhaps beyond practical limits ofmetrology equipment productivity.

But, in order to meet the increased data demands, only adding metrologyequipment or increasing metrology equipment productivity may notsuffice. Moreover, it may not solve all problems such as obtaining denseCD, focus and/or overlay profiles across a substrate in a timely manner.

So, metrology efficiency is desirable. This is to obtain, e.g., higherdensity of data per substrate and data for a higher number of substratesper lot.

Therefore, in an embodiment, there is provided a method to, e.g., helpimprove metrology efficiency. In the method, metrology data frommultiple sources is combined and manipulated in order to derive accurateestimated values of one or more patterning process parameters (e.g., CD,focus, overlay, edge placement, etc.) for each of a plurality oflocations across a substrate. In an embodiment, then, there is provideddense metrology data (e.g., for each square mm) for, e.g., all of thesubstrates processed in a patterning process and for, e.g., all of thelayers processed on such substrates in the patterning process.

In effect, in an embodiment, the results of the method is a “virtual” oremulated distribution of values of one or more patterning processparameters across the substrate, which is achieved through suchcombination of various metrology data. This method can offer then anefficient method for hybrid metrology for one or more patterning processparameters (e.g., focus, CD, overlay, etc.). And, while embodimentsherein will consider primarily particular examples of patterning processparameters namely focus, CD and overlay, it will appreciated that one ormore other or additional patterning process parameters can be thesubject of the techniques herein.

As noted above, the method involves combination of metrology and otherdata from various sources. In an embodiment, the method involvescombining measurements of a patterning process parameter of interestwith data from one or more devices in the patterning process, such asdata from one or more sensors of the lithographic apparatus. Thiscombination of data will then be used to predict on-product performancein the form of, e.g., a patterning process parameter, such as CD,overlay, focus, pattern shift, edge placement (e.g., edge placementerror), etc. and/or a parameter derived therefrom, such as yield,defects (e.g., risk of defect, defect counts, etc.), etc.

Thus, a principle underlying the method is to isolate and estimateindividual root-causes of the change of a patterning process parameterof interest which are then combined to compute the on-productperformance. The goal is to use as much of the available information aspossible to avoid ever increasing amounts of off-line (and/or on-line)metrology to determine a patterning process parameter of interest usingtools such as described in respect of FIGS. 3-6.

Thus, in an embodiment, it is desirable to identify the variouscontributions to the change of a patterning process parameter ofinterest (such as CD error, focus error, overlay, etc.). Thosecontributions can then be used in various combinations to achieve adesired estimate of the on-product performance. Typically, thosecontributions will be an error and/or a residual. For example, a devicemay produce an error in making a correction, which can then realize in achange of the patterning process parameter of interest. As anotherexample, a sensor system may measure an error, which error is orcontributes to a change of the patterning process parameter. As afurther example, a device or a mathematical model used to determine asetting of the device may not be able to realize a certain desired orbest physical effect (e.g., a difference between a desired physicalcorrection and the physical correction that can be achieved by a device,a difference between a desired physical effect such as dose, focus, etc.and the physical effect than can be achieved by a device, a differencebetween a desired physical correction or effect and the correction oreffect capable of being determined by a mathematical model, etc.) andthus realize a residual that is or contributes to a change of thepatterning process parameter. In an embodiment, a contribution can bedetermined experimentally or empirically.

Each of these contributions to a patterning process parameter ofinterest as spatially distributed across a die, a field or a substratecan then be characterized as a fingerprint. And, similarly, the combinedcontributions across the die, the field or the substrate can becharacterized as a fingerprint.

So, a plurality of these contributions can be combined to yield aderived fingerprint. For example, a focus fingerprint on a productsubstrate can be, for instance, a composite of focus contributions dueto unflatness of that substrate, a focus error associated with theprojection system of the lithographic apparatus during the substrate'sexposure, a height error made by the substrate position control loopduring exposure, and a residual fingerprint of the focus setup of thelithographic apparatus. An example of this is described below in respectof FIG. 9.

Similarly, a derived or measured fingerprint can have one or morefingerprints removed therefrom to yield a (further) derived fingerprint.For example, a measured focus fingerprint of a substrate can haveremoved therefrom the focus contributions of unflatness of thatsubstrate, a focus error associated with the projection system of thelithographic apparatus during the substrate's exposure, a height errormade by the substrate position control loop during exposure, and aresidual fingerprint of the focus setup of the lithographic apparatus.This can yield a residual focus fingerprint due to errors not capturedby the removed fingerprints. An example of this is described below inrespect of FIG. 10.

Thus, in an embodiment, the method can, for example, break down afingerprint into individual contribution fingerprints and/or derive afingerprint by combining fingerprints.

So, referring to FIG. 8, an embodiment of the combination ofcontributions (fingerprints) is depicted. A change of a processingvariable 311 (e.g., in the focus context, a height error) may have acontribution 312 to a patterning process parameter 352 (e.g., in thecontext of focus, focus) for a pattern on a substrate and that a changeof a processing variable 321 (e.g. in the focus context, a residual ofthe focus setup) may have a contribution 322 to the patterning processparameter 352. Namely, the patterning process parameter 352 may havecombined contributions of changes of one or more processing variables.These contributions 312 and 322 may be simply additive (which mayinclude weighted or linear addition) or be combined by other functions(e.g., using (de)convolution, using a neural network, RMS addition,scaling, etc.). The patterning process parameter 352 may havecontributions of changes in other variables. So, with this realizationas discussed further hereafter, various contributions can be determinedor can be used to derive estimates of a patterning process parameter. Inan embodiment, the contribution 312 and/or 322 may be determined bymodeling the one or more applicable processing variables. Thecontribution 312 and/or 322 may be expressed as a function of the one ormore applicable processing variables. The function may be linear ornon-linear.

FIG. 9 schematically shows an example of obtaining a derivedcontribution 470 to a patterning process parameter of a substrate, thederived contribution being a combination of contributions (one or moreof which may be a derived contribution) of multiple processingvariables. In this case, the derived contribution 470 is (de)focus. So,the derived contribution 470 can be obtained using contributions ofmultiple processing variables such as focus error (FE) associated withthe projection system of the lithographic apparatus during thesubstrate's exposure 400, a height error (e.g., moving standarddeviation (MSD_(z))) made by the substrate position control loop duringexposure 410, and unflatness (P) of that substrate 420. Significantly,this data can be obtained from the lithographic apparatus and can be aby-product of producing a substrate as part of a patterning process.None of these identified contributions necessarily requires ameasurement of a feature patterned on the substrate using, for example,tools such as described in respect of FIGS. 3-6. The contributions canbe obtained, as applicable, by simulation, mathematical modeling and/ormeasurement/experimentation. For example, the contributions can beobtained by simulation based on physical models, empirical modelingand/or dedicated measurements.

So, in the focus case, an example of the contribution to focus ofprocessing variable 400 is shown as contribution 430, an example of thecontribution to focus of processing variable 410 is shown ascontribution 440, and an example of the contribution to focus ofprocessing variable 420 is shown as contribution 450. Each of thesecontributions is then combined together 460 to realize derivedcontribution 470. While element 460 (and other elements in the Figures)shows a plus sign, the operation at 460 need not be addition, e.g., itcan be a multiplication, convolution, through use of a neural networketc. The operation may be different for one or more contributions thananother one or more contributions (e.g., an addition of 430 to 440 and aconvolution of the sum with contribution 450). In an example, thecombined contribution can be expressed as F(x, y)=a₁*F(FE)(x,y)+b₁*F(MSD_(z))(x, y)+c₁*F(P)(x,y)+ . . . . The various functions canbe obtained by simulation, mathematical modeling and/ormeasurement/experimentation. Moreover, there may be cross terms that arenot shown here (such as focus as a function of FE times MSD, etc.). Toobtain an absolute value of focus, a nominal value or simulated value ofthe focus can be combined with the contributions. The coefficients suchas a₁, b₁, c₁ are sensitivities of the focus with respect to therespective processing variables or their functions. In this example, thecontributions are across a substrate but in an embodiment, one or moreof the contributions may per die/field (which could then be repeatedacross the substrate depending on, e.g., applicable conditions at eachof the instances). As noted above, the contribution 470 may becharacterized as a fingerprint since it can be spatially defined acrossthe substrate/die/field. Further, the contribution's translation into anabsolute value may be characterized as a fingerprint since it can bespatially defined across the substrate/die/field. As will beappreciated, data from processing of multiple substrates using thepatterning process can be used to derive the respective contributions.This data can already be available since it could be the by-product ofprocessing the substrates.

Now, in the context of CD, the same technique described in respect ofFIG. 9 can be used. For example, the derived contribution 470 to CD canbe the combination of contributions (which can include a derivedcontribution) attributable to multiple processing variables such asfocus (F) 400, moving standard deviation (MSD_(z)) 410 of movement ofthe substrate in the normal direction of the substrate, and movingstandard deviation (MSD_(x)) 420 of movement of the substrate in adirection parallel to the substrate. So, in this case, an example of thecontribution to CD of focus (F) 400 would be contribution 430, anexample of the contribution to CD of moving standard deviation (MSD_(z))410 would be contribution 440, and an example of the contribution to CDof moving standard deviation (MSD_(x)) 420 would be contribution 440.Each of these contributions is then combined together 460 to realizederived contribution 470. In an example, the combined contribution canbe expressed as CD(x,y)=a₁*CD(F²)(x,y)+b₁*CD(MSD_(x))(x,y)+c₁*CD(MSD_(z) ²)(x,y)+ . . . .Moreover, there may be cross terms that are not shown here and therelations may be different (e.g., a relation, such as focus and/or MSDz,may not be purely quadratic, and could have linear and 3^(rd) orderterms). In an embodiment, the contributions 430, 440, 450 may berespectively focus (F) 400, moving standard deviation (MSD_(z)) 410 andmoving standard deviation (MSD_(x)) 420 distributions in which case a CDmodel would be used to combine them into a CD distribution. Moreover,there may be cross terms that are not shown here (such as CD as afunction of F times MSD, etc.). To obtain an absolute value of CD, anominal value or simulated value of the CD can be combined with thecontributions. The coefficients such as a₁, b₁, c₁ are sensitivities ofthe CD with respect to the processing variables or their functions.

Applying the principles described above, FIG. 10 schematically shows anexample of obtaining a derived contribution 510 from patterned substratemetrology data for a patterning process parameter of interest of asubstrate by removing a contribution to the patterning process parameterof interest. Patterned substrate metrology data in this context arevalues of a parameter of interest obtained by measuring a feature (e.g.,a device pattern feature, a metrology target separate from the devicepattern, etc.) on substrate that is at least partially processed by thepatterning process. Such metrology data can typically be obtained usingmetrology or inspection tools such as described in respect of FIGS. 3-6.

Patterned substrate metrology data 500 for a parameter of interest mayhave at least two contributions. So, one or more contributions withinthe patterned substrate metrology data can be obtained by removing oneor more other contributions within the patterned substrate metrologydata. Thus, a contribution 510 may be obtained by removing 505 acontribution 520 from the patterned substrate metrology data 500. Whileelement 505 (and other elements in the Figures) shows a minus sign, theoperation at 505 need not be subtraction, e.g., it can be amultiplication, (de)convolution, through use of a neural network, etc.Contribution 520 can be a derived contribution, such as contribution470, or can be a contribution derived from other data, such as any oneor more of contributions 430, 440 and 450. Further, multiplecontributions can be removed. For example, optional contribution 540,associated with a processing variable 530, can be removed from thepatterned substrate metrology data 500 along with contribution 520. Aswill be appreciated, data from processing of multiple substrates usingthe patterning process can be used to obtain the patterned substratemetrology data.

In an embodiment, the patterned substrate metrology data is from apattern separate from a device pattern, for example a metrology featureof at a non-functional area of a die, between dies or on a testsubstrate. So, for example, the contribution of one or more processingvariables can be removed from such metrology data, thereby obtaining aremaining contribution of one or more processing variables to suchmetrology data. The comparable contribution to metrology data of adevice pattern on the same or different substrate can then be obtainedbased on the remaining contribution, without the need of actuallyobtaining the metrology data from the device pattern. For example, thecontribution to the metrology of the device pattern may be estimated tobe the same as the remaining contribution because the applicable one ormore processing variables have comparable effect to the device patternand the separate pattern. In an embodiment, the separate pattern is apattern for testing purpose (e.g., a metrology target) and performingmetrology on the separate pattern does not impact a device pattern onthe substrate.

Therefore, by combining contributions and/or removing contributions frompatterned substrate metrology data, estimates of a parameter of interestof a substrate can be obtained without necessarily having to obtainpatterned substrate metrology data for that substrate. This is done byrecognizing the nature of the various contributions.

In an embodiment, a contribution of one or more processing variables maybe apparatus (e.g., lithographic apparatus) specific; that is, thecontribution is specific to a certain actual apparatus or combination ofapparatuses. Thus, in an embodiment, the contribution of the one or moreprocessing variables may be used repeatedly across every substrate.Therefore, the contribution of one or more processing variables may bepre-characterized and obtained from a database for variouscombination/removal processes. The contribution may be apparatusspecific as a whole or a specific part (e.g., etch chamber) of theapparatus. Examples of such variables may include, but are not limitedto, various characteristics of a process upstream or downstream topattern transfer in the lithographic apparatus, such as spin coating,post exposure bake, development, etching, deposition, doping, and/orpackaging.

In an embodiment, a contribution of one or more processing variables isnot specific to a particular substrate (and so can be used acrosssubstrates). Thus, the contribution of one or more processing variablesmay be pre-characterized and obtained from a database later for variouscombination/removal processes. This contribution of one or moreprocessing variables can be applied to a specific substrate by combiningit with data of the one or more variables for the specific substrate anda sensitivity relationship. Examples of such variables may include, butis not limited to, variables of the illumination, projection system,focus, dose, bandwidth, exposure duration, a characteristic of highfrequency stage movement (e.g., moving standard deviation (MSD) ofmovement of the substrate stage, moving average of the movement of thesubstrate stage, frequency, amplitude, etc.), a high frequency laserbandwidth change (e.g., frequency, amplitude, etc.), a high frequencylaser wavelength change, and/or flatness of the substrate.

In an embodiment, the contribution of one or more processing variablesmay be substrate specific. For example, the contribution may bedetermined for each substrate or a specific group of substrates.Examples of such variables may include, but are not limited to,substrate geometry (height map, deformation map), substrate processingconditions, variables of the illumination, variables of the projectionsystem, focus, dose, bandwidth, exposure duration, a characteristic ofhigh frequency stage movement (e.g., moving standard deviation (MSD) ofmovement of the substrate stage, moving average of the movement of thesubstrate stage, etc.), a high frequency laser bandwidth change (e.g.,frequency, amplitude, etc.), a high frequency laser wavelength change,and/or flatness of the substrate.

In an embodiment, the contribution of one or more processing variablesmay be pattern or patterning device specific; that is, the contributionis specific to a certain actual patterning device or specific pattern tobe provided by a patterning device. This contribution can be furthersubstrate independent. Thus, the pattern or patterning device specificcontribution may be pre-characterized and obtained from a database laterfor various combination processes. Examples of such variables mayinclude, but are not limited to, patterning device feature CD, a shapeand/or location of an assist feature, an adjustment applied by aresolution enhancement technique (RET), etc.

In an embodiment, the contribution associated with different processingvariables may have different spatial uniformity. For example, thecontribution of some processing variables may be essentially spatiallyuniform across the entire substrate, while the contribution of someother processing variables may be not so spatially uniform across theentire substrate. This difference may be attributed to the differentnature of the processing variables. For example, the contribution of oneor more processing variables associated with the resist layer,development of the resist layer, and/or etching of the substrate tend tobe essentially spatially uniform because the entire substrate is usuallycoated with the resist layer, developed or etched at a same time andunder a same condition, or tends to be symmetric because of, forexample, rotation of the substrate during a number of these processes.For example, the contribution of one or more processing variablesassociated with the pattern transfer or the lithography apparatus tendsto be less spatially uniform because the pattern transfer tends to belocation specific and the one or more processing variables may changebetween pattern transfer for one location and pattern transfer foranother location. Therefore, if the contribution that is not essentiallyspatially uniform can be removed from patterned substrate metrologydata, an essentially spatially uniform contribution can be obtained fromthe patterned substrate metrology data.

So, in a specific example, processing variable data can be gathered fromthe lithographic apparatus for each point exposed on the substrate, suchas leveling information, moving average (MA) of movement of thesubstrate, MSDxyz, dose, laser bandwidth, pupil shape, etc. This data istypically already available in a lithographic apparatus, e.g., indiagnostic files. From this data, the contribution described above canbe generated using a model for the parameter of interest that describesthe sensitivity of the parameter of interest to the one or moreprocessing variables. The one or more sensitivities can be obtained fromsimulation or from experiments. The contribution generated in thisfashion is what would be expected to be seen during a measurement afterresist development, assuming the track and resist model calibrationwould be perfect. Once the substrate is measured, e.g., after develop orafter etch, the contribution is removed from patterned substratemetrology data. The remaining contribution is now the contribution bythe pre- or post-pattern transfer process (e.g., by the track and/oretch apparatus, which is generally interfield) and the patterning device(intrafield). The lithographic apparatus errors would have beencorrected from the patterned substrate metrology data. Similarly, thepatterning device contribution may be measured and its contributionremoved to leave the contribution by the pre- or post-pattern transferprocesses. A contribution can be removed per process flow (e.g., acombination of patterning process steps and/or apparatus used) or perparticular apparatus or part thereof (e.g., etch apparatus or etchchamber).

So, through these techniques, contributions to a parameter of interestcan be obtained through modeled relationships or by removing knowncontributions from patterned substrate metrology data. Moreover, one ormore contributions can be apparatus specific but also substrateindependent. But one or more other contributions can be substratespecific. Thus, by appropriate mixing and matching of contributions, anestimate of a parameter of interest at a certain point in the patterningprocess can be estimated.

Therefore, some specific examples of the application of thesecontributions will now be described in the context of focus, CD andoverlay to determine an estimate of the respective focus, CD and overlayfor a substrate. As will be appreciated, additional or other parametersof interest can be processed and estimated.

To enable these examples, various data are used. For example, thelithographic apparatus has significant metrology capability integratedtherein that is used for pattern transfer control. Examples of suchintegrated metrology are position measurement devices (e.g., sensor IF)of the substrate and/or patterning device for servo control, a levellingsensor (e.g. sensor LS) for measurement of the substrate surface forlevelling control, an alignment sensor (e.g., sensor AS) to measure theorientation, position and/or deformation of the substrate to enableoverlay control, and/or an aberration sensor (e.g., the shearinginterferometer described above) in order control the wavefront of theprojection system. The lithographic apparatus will use data from thesesensors for control at a level where its overall CD, overlay, and/orfocus budgets are satisfied but at the same time also keep track ofresiduals and/or errors that are left after control. These residualsand/or errors may be used to calculate what CD, overlay, and/or focuserror is made during pattern transfer, i.e. the lithographic apparatus'contribution to the CD, overlay, and/or focus fingerprints. As will beappreciated, other apparatuses used in the patterning process may havesimilar information for the applicable metrology of the apparatus.

Further, lithographic apparatus setup or control can use one or moremathematical models to determine the respective calibration or controlcorrection. However, such one or more models may have a built-inassumption or limit leading to a non-zero residual error. Such a modelresidual can be used to calculate what CD, overlay, and/or focus erroris made, i.e. the model's contribution to the CD, overlay, and/or focusfingerprints. As will be appreciated, other apparatuses used in thepatterning process can have similar model information.

Further, a lithographic apparatus may be setup by using in-resistmeasurements to help remove any global and local fingerprints of one ormore parameters (e.g., focus, overlay, etc.). But the global fingerprintcan drift over time from the last time calibration was performed. Formonitoring and control of this setup state, monitor substrates can beexposed and measured to monitor the global fingerprint. The monitorsubstrates can be basic substrates with a well-defined pattern in thesubstrate onto which a resist layer is applied, exposed with a patternin relation to the well-defined pattern, developed and then measured.Once measured, the resist on the monitor substrate can be stripped toleave the well-defined pattern so that a new layer of resist can beapplied. Based on those measurements, corrections can be made to thelithographic apparatus and so those corrections need to be factored indetermining the contributions. In an embodiment, the monitor substratescan be used to determine overlay by using the well-defined patternand/or to determine focus by using the resist pattern.

Turning to a focus example, the technique involves essentially two mainparts. A first part is effectively a setup process to determine anunderlying focus contribution of the lithographic apparatus that is notreflected in one or more types of lithographic apparatus processingvariables that are used to determine an estimate of focus for aparticular substrate in the estimation process. The second part is theestimation process of using a focus contribution associated with thoseone or more types of lithographic apparatus processing variables for thesubstrate under consideration to determine the estimate of focus for theparticular substrate.

So, in the setup process according to an embodiment, patterned substratefocus metrology data is obtained for one or more substrates and then thecontributions of one or more types of lithographic apparatus processingvariables are removed similarly to as described above in FIG. 10. Onetype of contribution that can be removed is the focus contribution of asubstrate height residual or error map associated with, e.g., thelevelling sensor of the lithographic apparatus. A further type ofcontribution that can be removed is the focus contribution of projectionsystem image plane deviation (IPD), which can be obtained, e.g., from ashearing interferometer and/or a projection system model residual. Afurther type of contribution that can be removed is the focuscontribution of patterning device and/or substrate servo control (e.g.,MA), which can be obtained from the applicable positioner, a positionmeasurement device (e.g., sensor IF) and/or a residual of a servocontrol model. As discussed above, the translation from a processingvariable to the focus contribution can be determined through simulation,mathematical modelling and/or experimentation.

As needed, the contribution fingerprints can be re-gridded to a samegrid (which can be the same as the grid of one of the contributionfingerprints or a different grid). Similarly, the contributionfingerprints can be re-gridded to the patterned substrate metrologydata, or vice versa. In an embodiment, the re-gridding comprises upsampling or down sampling.

In an embodiment, a filtering (e.g., moving average, deconvolution, FFT,etc.) is applied to a contribution, desirably before combining it withanother contribution.

In an embodiment, the underlying focus contribution of the lithographicapparatus can effectively be determined once and used for various focusestimates and thus the amount of metrology can be significantly reducedcompared to measuring each substrate. In an embodiment, the patternedsubstrate focus metrology data can be obtained by relatively sparsesampling of locations on the substrate (e.g., 500 targets or less on asubstrate) and/or of the number of substrates from one or more lots(e.g., 10 or less substrates from a lot of 25 or more substrates).

In an embodiment, the patterned substrate focus metrology data can be ameasured focus fingerprint of a monitor substrate as described above.Thus, data that is already being captured can be used. So, the measuredfocus fingerprint can be corrected for the lithographic apparatus impactas derived from lithographic apparatus sensor information, such as thefocus contribution of projection system image plane deviation (IPD), thefocus contribution of the substrate height residual or error map, and/orthe focus contribution of patterning device and/or substrate servocontrol, to arrive at the underlying focus contribution of thelithographic apparatus.

The underlying focus contribution of the lithographic apparatus is thenstored for use in on-product estimations of focus. The underlying focuscontribution of the lithographic apparatus can be determined formultiple lithographic apparatuses. The underlying focus contribution ofthe lithographic apparatus can be determined for a particularcombination of devices of the lithographic apparatus used. For example,the lithographic apparatus may have more than one substrate table onwhich the substrate could be exposed and so the underlying focuscontribution of the lithographic apparatus can be determined for aspecific combination and/or multiple combinations of devices used.

Then, for the on-product estimation, the errors or residuals of one ormore types of lithographic apparatus processing variables relevant tofocus are obtained for a substrate of interest and the focuscontribution thereof is determined. For example, the focus contributionof projection system image plane deviation (IPD), the focus contributionof the substrate height residual or error map, and/or the focuscontribution of patterning device and/or substrate servo control can beobtained for the substrate of interest. A further type of contributionthat can be added is the focus contribution of patterning device errorsattributable to the patterning device being used for the particularsubstrate of interest, which could be obtained by measurement. Thiscontribution may be particularly used if the applicable underlying focuscontribution of the lithographic apparatus was obtained without usingthe patterning device for the substrate of interest.

Further, an applicable underlying focus contribution of the lithographicapparatus, as described above, is obtained. Then, the applicableunderlying focus contribution of the lithographic apparatus is combined,similarly to as described above in respect of FIG. 9, with the one ormore specific focus contributions of the substrate of interest to obtainan estimated focus fingerprint for the substrate of interest. So, anestimate of focus error can be determined at any, or almost any,location on any substrate.

Now, turning to a CD example, in principle, there are a number ofprocessing variables that can cause CD variation in a substrate. In thisembodiment, certain CD variations across the substrate are considered.In particular, there are considered the CD variation contribution inrespect of focus, focus blur, dose, and overall process. The patterningdevice, which is an intrafield contributor to CD variation, can also beconsidered but will not be further described for convenience only.

The focus contribution to CD can be based on focus contribution asdescribed above, specifically the combination of the underlyinglithographic apparatus focus contribution with the focus contributionsof one or more processing variables of the lithographic apparatus for asubstrate under consideration. This dense focus information can be, inprinciple, converted into a ACD contribution across the field and/oracross substrate for any pattern feature given that, for example, theBossung behavior of the feature (after-litho and/or after-etch) can beknown through experiment or simulation. Hence, for any location (x, y)on the substrate with a focus value, a CD value can be calculatedcorresponding to that substrate location (x, y):

CD(HDFM_(x, y)) = Φ₁(HDFM_(x, y))

wherein HDFM corresponds to a focus map such as the derived high densityfocus map as described above in the focus example.

The focus blur contribution to CD can be obtained using lithographicapparatus data, such as servo information (e.g., MSD in the zdirection). The focus blur information can be converted into a ΔCDcontribution across a scan direction and across the substrate. Thisfocus blur data to CD conversion is also feature specific and can beknown through experiment or simulation:

CD(fblur_(x, y)) = Φ₂(fblur_(x, y))

wherein fblur corresponds to focus blurring.

The dose contribution to CD is due to the lithographic apparatus's dosevariation (e.g. determined by a dose mapping system). The dose variationacross the substrate during exposure can be translated into a ΔCDcontribution using a suitable dose sensitivity of the applicablefeature, which can be known through experiment or simulation:

CD(dose_(x, y)) = Φ₃(dose_(x, y))

The overall process contribution to CD is a CD variation arising fromvarious process steps as part of the patterning process separate fromthe pattern transfer alone. Thus, in an embodiment, the overall processcontribution is the state of CD variation after the final etch step andnot attributable to the various other CD variations considered inestimating the CD variation. Thus, in an embodiment, this contributionis the cumulative effect of all unaccounted for process variationsarising from, e.g., film deposition variation, baking and/or developingvariation, and/or etch process variation. Examples of processingvariables that contribute to the overall process contribution to CD mayinclude a characteristic of structures under a resist layer, chemicalcomposition and/or physical dimension of the resist layer, and/or acharacteristic of one or more processes upstream, or downstream, to thepattern transfer in a lithography apparatus, such as spin coating, postexposure bake, development, etching, deposition, doping and/orpackaging. And, while the overall process contribution to CD isdescribed in terms of after etch, the overall process contribution canbe obtained for different points in the patterning process, e.g.,obtained after development but before etch.

So, similar to the setup process of the focus example, all of these ΔCDcontributions due to focus, focus blur and dose can be used andsubtracted from substrate CD measurements to estimate the overallprocess contribution. That is, in an embodiment, an after etch overallprocess contribution can be generated from an anchor feature CDmeasurement after etch, from which the ΔCD contributions for focus,focus blur and dose (for the anchor feature) are removed. As noted, theoverall process contribution is estimated from a suitable anchorfeature. So, in an embodiment, the overall process contribution forother features can be determined from the anchor feature. For example,the remainder of the overall process contribution can be expressed as aproportion of the anchor feature's characteristic. Where the overallprocess contribution is obtained for a different point in the patterningprocess, e.g., obtained after development but before etch, an afterdevelop but before etch CD measurement can be used.

In an embodiment, the overall process contribution can effectively bedetermined once and used for various CD estimates and thus the amount ofmetrology can be significantly reduced compared to measuring eachsubstrate. In an embodiment, the patterned substrate focus metrologydata can be obtained by relatively sparse sampling of locations on thesubstrate (e.g., 500 targets or less on a substrate) and/or of thenumber of substrates from one or more lots (e.g., 10 or less substratesfrom a lot of 25 or more substrates).

The overall process contribution is then stored for use in on-productestimations of CD. The overall process contribution can be determinedfor a particular and/or multiple apparatus configurations (e.g., one ormore specific etch chambers, one or more specific combinations of etchchamber and bake plate, one or more specific combinations of substratetable and etch chamber, etc.).

Then, similar to the focus estimation step described above, anestimation of on-product CD can be obtained. In an embodiment, theerrors or residuals of one or more types of lithographic apparatusprocessing variables relevant to CD are obtained for a substrate ofinterest and the CD contribution thereof is determined. For example, theCD contribution of focus, focus blur and/or dose can be obtained for thesubstrate of interest. A further type of contribution that can be addedis the CD contribution of patterning device errors attributable to thepatterning device being used for the particular substrate of interest,which could be obtained by measurement.

Further, an applicable overall process contribution to CD, as describedabove, is obtained. Then, the applicable overall process contribution toCD is combined, similarly to as described above in respect of FIG. 9,with the one or more specific CD contributions of the substrate ofinterest to obtain an estimated CD fingerprint for the substrate ofinterest. So, an estimate of CD error can be determined at any, oralmost any, location on any substrate.

Moreover, the estimate can be obtained for one or more specific patternfeatures of interest on a substrate, such as a hot spot. As noted above,the overall process contribution to CD was determined for a particularanchor feature, but can be scaled for the one or more specific featuresof interest. Further, the CD contribution of one or more types oflithographic apparatus processing variables (such as focus, focus blurand/or dose) can be computed based on an appropriate sensitivity for theone or more specific features between the CD variation and the one ormore types of lithographic apparatus processing variables. Suchsensitivity can be obtained, e.g., by simulation and/or experiment.Thus, multiple CD substrate fingerprints can be obtained, each for adifferent hot spot or other feature of interest of a pattern.

The methodology can be improved, e.g., with more parameters in one ormore pertinent models, e.g., patterning device and/or aberration models.The methodology can be extended by, e.g., estimating the overall processcontribution by breaking it up into different contributors, e.g.deposition, lithography, and/or etch with different sensitivities todifferent features.

In an embodiment, a dose correction applied as part of the patterningprocess can be corrected for in the results. For example, the lithocellmay apply a dose correction using, for example, ASML's Dosemappersystem. So, this correction is accounted for in the determination of theestimate of CD.

Turning now to an overlay example, data is used from at least twodifferent pattern transfers onto the substrate. The techniques aresimilar to those described above in respect of the focus and CDexamples.

This technique involves essentially two main parts. A first part iseffectively a setup process to determine an underlying overlaycontribution of the lithographic apparatus that is not reflected in oneor more types of lithographic apparatus processing variables that areused to determine an estimate of overlay for a particular substrate inthe estimation process. Optionally, an overall process overlaycontribution can also be determined similar to the overall process CDcontribution of the CD example discussed above. The second part is theestimation process of using an overlay contribution associated withthose one or more types of lithographic apparatus processing variablesfor the substrate under consideration for each of the at least twopattern transfers to determine the estimate of overlay for theparticular substrate.

So, in the setup process according to an embodiment, patterned substrateoverlay metrology data is obtained for one or more substrates and thenthe contributions of one or more types of lithographic apparatusprocessing variables for each of at least two pattern transfers areremoved similarly to as described above in FIG. 10. One type ofcontribution that can be removed is the overlay contribution of asubstrate height map obtained, for example, from the levelling sensor ofthe lithographic apparatus. A difference can be found for the substrateheight maps for two pattern transfers and then the difference can beconverted to an overlay value and thus the overlay contribution. Forexample, the Z height difference can be turned into X and/or Ydisplacements by considering the height difference as a warpage or bendof the substrate and using first principles to calculate the X and/or Ydisplacements (e.g., the displacement can be the variation in Z versusthe variation in X or Y times half the thickness of the substrate in,e.g., a clamped region of the substrate or the displacement can becalculated using Kirchoff-Love plate theory in, e.g., an unclampedregion of the substrate). In an embodiment, the translation of theheight to the overlay contribution can be determined through simulation,mathematical modelling and/or experimentation. So, by using suchsubstrate height information per pattern transfer, the overlay impactdue to a focus or chuck spot can be observed and accounted for.

A further type of contribution that can be removed is the overlaycontribution of patterning device and/or substrate servo control (e.g.,MA) in the X and/or Y directions (including rotation around Z), whichcan be obtained from the applicable positioner, a position measurementdevice (e.g., sensor IF) and/or a residual of a servo control model. Adifference can be found for the servo control values across thesubstrate for two pattern transfers and then the difference canrepresent the overlay contribution. Where needed, the translation fromservo control values to the overlay contribution can be determinedthrough simulation, mathematical modelling and/or experimentation.

A further type of contribution that can be removed is the overlaycontribution of projection system aberrations (which can be obtained,e.g., from a shearing interferometer) and/or projection system modelresidual. The translation from the aberrations and/or residual to theoverlay contribution can be determined through simulation, mathematicalmodelling and/or experimentation.

A further type of contribution that can be removed is the overlaycontribution of an alignment system model residual, which can beprovided by the lithographic apparatus. The translation from theresidual to the overlay contribution can be determined throughsimulation, mathematical modelling and/or experimentation. In anembodiment, the alignment system model residual can be different fordifferent pattern transfer steps and thus a combination/difference ofthe alignment system model residuals for the different pattern transfersteps can be used to obtain the overlay contribution. In an embodiment,the alignment model residual can be corrected for substrate height.

As needed, the contribution fingerprints can be re-gridded to a samegrid. Similarly, the contribution fingerprints can be re-gridded to thepatterned substrate metrology data, or vice versa.

In an embodiment, the underlying overlay contribution of thelithographic apparatus can effectively be determined once and used forvarious overlay estimates and thus the amount of metrology can besignificantly reduced compared to measuring each substrate. In anembodiment, the patterned substrate overlay metrology data can beobtained by relatively sparse sampling of locations on the substrate(e.g., 500 targets or less on a substrate) and/or of the number ofsubstrates from one or more lots (e.g., 10 or less substrates from a lotof 25 or more substrates).

In an embodiment, the patterned substrate overlay metrology data can bea measured overlay fingerprint of a monitor substrate as describedabove. Thus, data that is already being captured can be used. So, themeasured overlay fingerprint can be corrected for the lithographicapparatus impact as derived from lithographic apparatus sensorinformation, such as the overlay contribution of the projection system,the overlay contribution of the substrate height, the overlaycontribution of alignment model residual, and/or the overlaycontribution of patterning device and/or substrate servo control, toarrive at the underlying overlay contribution of the lithographicapparatus. In an embodiment, the measured overlay fingerprint data wouldbe captured once for a first pattern transfer of the product substrateand then captured against for a second pattern transfer (with rework ofthe monitor substrate between pattern transfers). In an embodiment, thepatterned substrate overlay metrology data is an overlay deltafingerprint obtained from the difference between the overlay fingerprintmeasured from the one or more monitor substrates after the first patterntransfer and the overlay fingerprint measured from the one or moremonitor substrates after the second pattern transfer. So, by exposing aset of monitor substrates at about the same time as product layers, thelithographic apparatus contribution to overlay in terms of short termdrift can be quantified. That is, with then overlay delta fingerprint,the lithographic apparatus contribution on interfield overlay due toshort term drift between the first and second pattern transfers can beobtained.

Optionally, where an after-etch overlay is desired, an etch processcontribution to overlay can be determined, which is an overlay variationarising from the etching. To obtain the etch process overlaycontribution, after-develop but before etch patterned substratemetrology data can be removed from after-etch patterned substratemetrology data to obtain the etch process overlay contribution. In anembodiment, the etch process overlay contribution can effectively bedetermined once and used for overlay estimates and thus the amount ofmetrology can be significantly reduced compared to measuring eachsubstrate. In an embodiment, the patterned substrate overlay metrologydata can be obtained by relatively sparse sampling of locations on thesubstrate (e.g., 500 targets or less on a substrate) and/or of thenumber of substrates from one or more lots (e.g., 10 or less substratesfrom a lot of 25 or more substrates). The etch process fingerprintinduced at a first or second pattern transfer could be deduced with adelta fingerprint between after develop but before etch overlaymeasurement and after etch overlay measurement after etch of the otherof the first or second pattern transfer, assuming the etch fingerprintafter each pattern transfer is the same.

The underlying overlay contribution of the lithographic apparatus (andthe optional etch process overlay contribution) is then stored for usein on-product estimations of overlay. The underlying overlaycontribution of the lithographic apparatus can be determined formultiple lithographic apparatuses. The underlying overlay contributionof the lithographic apparatus can be determined for a particularcombination of devices of the lithographic apparatus used. For example,the lithographic apparatus may have more than one substrate table onwhich the substrate could be exposed and so the underlying overlaycontribution of the lithographic apparatus can be determined for aspecific combination and/or multiple combinations of devices used. Theetch process overlay contribution can be determined for a particularand/or multiple apparatus configurations (e.g., one or more specificetch chambers).

Then, for the on-product estimation, the errors or residuals of one ormore types of lithographic apparatus processing variables relevant tooverlay are obtained for a substrate of interest and the overlaycontribution thereof is determined. For example, the overlaycontribution of the projection system, the overlay contribution of thesubstrate height, the overlay contribution of alignment model residual,and/or the overlay contribution of patterning device and/or substrateservo control, to arrive at the underlying overlay contribution of thelithographic apparatus can be obtained for the substrate of interest. Inan embodiment, only the overlay contribution of the substrate height isobtained.

Further, an applicable underlying overlay contribution of thelithographic apparatus, as described above, is obtained and optionallythe applicable etch process overlay contribution is obtained. Then, theapplicable underlying overlay contribution of the lithographic apparatus(and optionally the optional etch process overlay contribution) iscombined, similarly to as described above in respect of FIG. 9, with theone or more specific overlay contributions of the substrate of interestto obtain an estimated overlay fingerprint for the substrate ofinterest. So, an estimate of overlay can be determined at any almostlocation on any substrate.

In an embodiment, an overlay correction applied as part of thepatterning process can be corrected for in the results. For example, thelithocell may apply an overlay correction, e.g., based on themeasurements of the monitor substrates using, for example, ASML'sBaseliner system. So, this correction is accounted for in thedetermination of the estimate of overlay.

In an embodiment, in a multiple patterning process, it is desirable thatboth exposure and lithographic apparatus conditions, e.g., exposuredose, patterning device transmission, patterning device qualificationerrors, illumination settings, lithographic apparatus substrate clampingerrors, etc., are very similar between the first and second patterntransfer steps. Furthermore, the exposure and heating signature atintrafield level would be expected to be similar between the first andsecond pattern transfer steps and therefore such effects on overlayshould be small.

Further, in an embodiment, a plurality of the predictions can becombined. For example, an overlay prediction and CD prediction can becombined. For example, in a multiple patterning situation that createsstructures adjacent each other using different pattern transfer stepsand those structures have a gap between them, a combination of the CDone or more of the different pattern transfer steps as well as anoverlay for the different pattern transfer steps can give a betterprediction of a size of the gap than an overlay or CD estimate alone.

FIG. 11 then schematically shows a flow for a method, according to anembodiment. In particular, it shows how a generalized contribution, suchas the underlying focus contribution of the lithographic apparatus, theoverall process contribution to CD, and/or the underlying overlaycontribution of the lithographic apparatus (and optionally theapplicable etch process overlay contribution), can be applied tospecific information for a substrate of interest to obtain an estimateof a parameter of interest for the substrate. So, contribution 912corresponding to one or more processing variables of a particularsubstrate and, e.g., for a hot spot. This can be determined by modeling,from device information, etc. Further, a contribution 922 applicable toa plurality of substrates, such as the underlying focus contribution ofthe lithographic apparatus, the overall process contribution to CD,and/or the underlying overlay contribution of the lithographic apparatus(and optionally the applicable etch process overlay contribution), isobtained. The contribution 922 may be obtained used any of thetechniques described herein. The contribution 912 may be determined fora plurality of substrates (e.g., for every substrate of interest) whilethe contribution 922 may be used repeatedly across many substrates. Thecontribution 912 and the contribution 922 are combined to obtain anestimate 950 of the parameter of interest for, e.g., a hot spot, withoutnecessarily requiring obtaining patterned substrate metrology data forthe hot spot. In procedure 970, an action is taken, such as whetherthere is a defect at the hot spot, is determined based on the estimateof the parameter of interest.

Thus, device sensor data can be exploited to enhance in-resist and/orafter etch metrology to obtain a computed metrology that can, forexample, provide dense metrology per substrate without having to havedense sampling of substrates and/or providing metrology for many, if notevery, substrate without having to obtain patterned substrate metrologydata for each such substrate. Further, the dense computed metrology canenable, for example, higher order corrections. The computed metrologycan also enable greater control, including possibly per substratecontrol, without having to obtain patterned substrate metrology data foreach such substrate and/or without having to measure patterned substratemetrology data densely on substrates.

Moreover, the estimates from these computed metrology technique canenable various applications, such as patterning process control (e.g.,adjustment of one or more process variables), patterning processingmonitoring, fault detection, defect prediction, patterning processdesign, etc.

In an embodiment, a derived contribution (such as derived using FIG. 10)can be used to parameterize a mathematical model for determining thecontribution of change of one or more processing variables to aparameter of interest. That is, a mathematical model can be fittedagainst the derived contribution, thereby obtaining the values of one ormore parameters, constants, etc. of the mathematical model. So, as anexample, it is desirable to have a model and any sensitivitiesrepresented in the model to adapt to changes in a process and/orsubstrate stack. So, in an embodiment, a predicted substrate fingerprintfor every substrate that will be measured can be generated. For this, amodel of a parameter of interest can be established, e.g., for CD, amodel comprising CD=a1*DOSE+a2*FOCUS²+a3*MSDx+a4*MSDy+a5*MSDz+ . . . .With measurement of a substrate, the pre- and/or post-process (e.g.,track/etch) fingerprint and the patterning device fingerprint can beremoved. The remaining fingerprint measurements can be compared to thepredicted values. In this situation, there are now a set of equations(as many equations as measurement points) where the CD, dose, focus,MSD-xyz, aberrations, etc. are known. This set of equations can besolved for the sensitivities (a1, a2, . . . ) that are desired. Whenthis is performed for a number of substrates measured for a certaindevice pattern, there will be plenty of data to re-estimate thesensitivities desired. If data from multiple lithographic apparatusesare used and/or data from focus exposure matrix exposures are used inthe same fashion, sufficient variation in the input signals (e.g.,focus, dose, MSD, CD, etc.) can enable proper estimation ofsensitivities. Further, the technique can be applied to other parametersof interest such as depth of focus, exposure latitude, overlay, edgeposition, etc.

In an embodiment, a training algorithm could be used to add furtheraccuracy. For example, when the sensitivities for aberration are solved,a boundary condition can be taken into account that the aberration canonly vary over the slit and pre-filter the CD (or overlay) data beforefitting these sensitivities. In an embodiment, the sensitivities canbecome robust against variations in the patterning process byre-assessing them from time to time or continuously.

Referring back to FIG. 6 and its associated description, in anembodiment, one or more of the variables in the parameterized model 206can have a stronger impact on the computed radiation distribution thanone or more other variables. For example, a small percentage change ofone or more variables may result in a significant difference in thecomputed radiation distribution. Such a variable may be referred to as astrong variable. A strong variable may include, but is not limited to, acritical dimension of a feature. On the other hand, a significantpercentage change of one or more other variables may result in a smalldifference in the computed radiation distribution. Such a variable maybe referred to as a weak variable. A weak variable may include, but isnot limited to, the sidewall angle of a feature, a height of a feature,a thickness of a layer, resist loss during development, footing of afeature, a refractive index of a layer, an absorption of a layer, and/oran extinction coefficient of the layer.

Both strong and weak variables in the parameterized model 206 may beused by a user (e.g., a human, a control system, etc.) for evaluatingone or more steps of the patterning process. Specifically, one or moreweak variables may be useful to determine whether there is a defect onthe target 30′ or other pattern, which can be used in one or moreprocesses upstream, or downstream, to the pattern transfer in alithography apparatus, such as spin coating, PEB, development, etching,deposition, doping, and/or packaging. For example, when the sidewallangle of a pattern on the substrate exceeds a certain threshold, one ormore defects may likely be produced during subsequent etching. As such,a defect likely due to etching may be predicted before the etchingprocess takes place based on a value of sidewall angle of the pattern onthe substrate. Such examples are non-limiting.

However, it is challenging to determine the values of the weak variablesbased on the measurement directly. This is because the signals that maybe used to determine the values of the weak variables in the inspectionsystem are usually quite weak, and sometimes, too weak to be detected.In addition, it is difficult to provide a certain level of the accuracyof determining the values of weak variables particularly when there aremany variables in the parameterized model and the values of the strongvariables are unknown.

In order to obtain more accurate values of one or more weak variablesfor various uses (e.g., to predict a defect) through a reconstructionprocess as described in FIG. 6, it is desirable to determine the valuesof the one or more strong variables (e.g., a CD) in the parameterizedmodel outside of the reconstruction process per se.

FIG. 12 shows a flow of a method to determine values of a strongvariable on a substrate (which can avoid performing metrology of thestrong variable on the substrate) according to an embodiment. Theprocess can be applied to obtain values of a plurality of differentstrong variables. As shown, a fingerprint of the strong variable 1640for a substrate may be obtained by combining a first contribution 1610from a first group of one or more variables related to the lithographicapparatus (such as focus, dose, MSD, aberration, pupil shape, etc. andwhich can be spatially specified per die/field and repeated across thesubstrate under application conditions or spatially specified across thesubstrate), a second contribution 1620 from a second group of one ormore variables related to one or more fabrication processes prior to, orafter, pattern transfer in the lithographic apparatus (such as etch,development, etc. and which can be spatially specified across thesubstrate), and a third contribution 1630 from a third group of one ormore variables related to the patterning device used in the patterningprocess (such as mask CD, etc. and which can be spatially specified perdie/field and repeated across the substrate under application conditionsor spatially specified across the substrate). The fingerprint of thestrong variable 1640 can be obtained for any specific portion of thesubstrate, such as the portion of target 30′.

The first group of one or more variables related to the lithographicapparatus may be one or more variables as described above. The firstcontribution 1610 may be lithographic apparatus specific; that is, thefirst contribution 1610 is specific to a certain actual lithographicapparatus. In an embodiment, the first contribution 1610 is not specificto a particular substrate (and so can be used across substrates). Thus,the first contribution 1610 may be pre-characterized and obtained from adatabase later for the reconstruction process. This first contribution1610 can be applied to a specific substrate by combining it with data ofthe one or more variables for the specific substrate and a sensitivityrelationship. The first contribution 1610 may be substrate specific. Forexample, the first contribution 1610 may be determined for eachsubstrate or a specific group of substrates so that the fingerprint ofthe strong variable 1640 is specific to the substrate or group ofsubstrates. Examples of the first group of variables may include, but isnot limited to, variables of the illumination, projection system, focus,dose, bandwidth, exposure duration, a characteristic of high frequencystage movement (e.g., moving standard deviation (MSD) of movement of thesubstrate stage, moving average of the movement of the substrate stage,etc.), a high frequency laser bandwidth change (e.g., frequency,amplitude, etc.), a high frequency laser wavelength change, and/orflatness of the substrate.

The third group of one or more variables related to the patterningdevice may be one or more variables as described above. The thirdcontribution 1630 may be pattern or patterning device specific; that is,the third contribution 1630 is specific to a certain actual patterningdevice or specific pattern to be provided by a patterning device. Thethird contribution 1630 can be substrate independent. Thus, the thirdcontribution 1630 may be pre-characterized and obtained from a databaselater for the reconstruction process. Examples of the third group ofvariables may include, but is not limited to, mask CD, a shape and/orlocation of an assist feature, an adjustment applied by a resolutionenhancement technique (RET), etc.

The second group of one or more variables related to one or morefabrication processes prior to, or after, pattern transfer in thelithographic apparatus may be one or more variables as described above.Like the first contribution 1610, the second contribution 1620 may besubstrate independent or substrate dependent. In an embodiment, thesecond contribution 1620 may be used repeatedly across every substrate.Therefore, the second contribution 1620 may be pre-characterized andobtained from a database during the reconstruction process. Examples ofthe second group of one or more variables may include, but is notlimited to, various characteristics of a process upstream or downstreamto pattern transfer in the lithographic apparatus, such as spin coating,PEB, development, etching, deposition, doping, and/or packaging.

The first contribution 1610, the second contribution 1620 and/or thethird contribution 1630 may be characterized by experimentation or takenfrom prior production data, e.g., using the flows of any of FIGS. 8-11.In an embodiment, the third contribution 1630 (i.e., the patterningdevice fingerprint) may be obtained by measuring the patterning devicedirectly using a patterning device metrology tool.

After the fingerprint 1640 of the strong variable is determined, a valueof the strong variable 1660 may be obtained by combining the fingerprint1640 of the strong variable and a certain value 1650 of the strongvariable. In an embodiment, the certain value of the strong variable canbe a nominal design value. In an embodiment, the strong variable may bean average of a group of measurements of the strong variable on thesubstrate. The group of measurements of the strong variable may beperformed with respect to a same feature in two or more dies on thesubstrate.

Given the values of one or more strong variables in the parameterizedmodel (e.g., by fixing the values of the one or more strong variables,or restricting the value of each of the one or more strong variableswithin a predetermined range (e.g., within 10%, within 5%, within 3%,within 1%), one or more weak variables may be adjusted until thecomputed radiation distribution is substantially similar to the measuredradiation distribution, or a difference between the computed radiationdistribution and the measured radiation distribution is within apredetermined tolerance threshold. When the computed radiationdistribution is substantially similar to the measured radiationdistribution, or the difference is within the predetermined tolerancethreshold, values of the one or more weak variables may be output.

As described above, the values of one or more weak variables may be usedto predict whether there would be a defect due to one or more downstreamprocesses after exposure, e.g., PEB, development of a resist layer,etching, deposition, doping, and/or packaging. If a defect is predicted,a value of one or more of the variables of the first group of one ormore variables, the second group of one or more variables, and/or thethird group of one or more variables may be adjusted to obtain a newfingerprint of the strong variable. This is done so that a new set ofvalues of one or more weak variables may be reconstructed using theprocess described above. Such adjustment may be performed iterativelyuntil no defect is predicted based on a new set of values of the one ormore weak variables.

In a further application of the contribution/fingerprint discussedabove, a contour of a pattern can be predicted using one or morecontributions/fingerprints. In this context, a contour is an outline ofa shape of a feature of a pattern transferred to a substrate. A contourcan be, for example, visualized by processing an image (e.g., scanningelectron microscope image) of a substrate to extract the outer boundaryof shape of a pattern feature transferred to the substrate. But acontour can also be generated by mathematical processes (e.g.,simulation) to create an electronic representation of a pattern featureas it is expected to be transferred to the substrate. While a contourwill typically be in the form of a line, the contour as used herein canbe generalized more to data describing the boundary of the feature. Thecontour need not be continuous; that is, the outline and/or data can bediscontinuous around the feature if the discontinuous outline and/ordata sufficiently describes the boundary of the feature. In anembodiment, the contour can be two-dimensional (i.e., defined a plane)or three-dimensional. In an embodiment, the contour can extend in aplane substantially parallel to the surface of the substrate on whichthe pattern is formed. In an embodiment, the contour can extend in aplane substantially perpendicular to the surface of the substrate onwhich the pattern is formed; in which case it can be characterized as aprofile and can be of two-dimensional or three-dimensional form.

To predict the contour, one or more contributions/fingerprints can beobtained as described herein and used to select a certain nominalcontour and/or modify a nominal contour, in order to arrive at apredicted contour. Referring to FIG. 13, an embodiment of a flowchart ofa method of prediction of a contour is depicted. At 1700, a nominalcontour of the feature of a pattern is determined. In an embodiment, thenominal contour is a contour as expected in resist. In an embodiment,the nominal contour is a contour as expected in a developed resist.

In an embodiment, the nominal contour can be obtained by mathematicalcalculation via a model and/or simulation. In an embodiment, thesimulator or model, e.g., a simulator such as ASML's Tachyon product,can determine an expected contour of a feature of a pattern atapplicable design values for one or more processing variables for thepatterning process of the feature. This contour obtained by calculationcan then be designated as a nominal contour. Similarly, the simulator ormodel can determine contours at various different values of the one ormore processing variables (e.g., one or more optical settings orconditions such as different focus settings or conditions, differentdose settings or conditions, different projection system aberrationsettings or conditions, different illumination pupil shape settings orconditions, etc.) to obtain a plurality of contours of the feature, eachcontour at a different value of the one or more processing variables.These contours obtained by calculation can then be designated as nominalcontours with each nominal contour associated with a different value ofthe one or more processing variables. In an embodiment, the nominalcontours are determined for different focus settings or conditions andso each of the nominal contours can be associated with a different focussetting or condition (such as a certain variance from best focus). Whilethe description below focuses on focus settings or conditions, thenominal contours can be determined for different settings or conditionsthan focus and can be determined for various combinations of settings orconditions.

In an embodiment, the impact of the one or more processing variables forwhich the nominal contour is determined on one or more other processingvariables, is evaluated. In an embodiment, the one or more otherprocessing variables evaluated are one or more processing variables thathave impact on the shape and/or size of the contour. So, in anembodiment, where the nominal contour is determined for a focus setting,the impact of focus on one or more other processing variables (such asCD) is determined. In an embodiment, this impact can be determined usinga focus exposure matrix (FEM) type process, wherein a certain pattern isevaluated at at least different focus settings or conditions. The CD atthose different focus settings or conditions can then be determined soas to evaluate how much a change in CD is due to focus. In anembodiment, the impact described above can be determined experimentallyusing one or more processed substrates which are then measured by ametrology tool. In an embodiment, the impact described above can bedetermined using a simulator.

Additionally or alternatively to determining the nominal contour(s) bycalculation, in an embodiment, the nominal contour(s) can be obtained byexperiment. For example, the feature can be created on one or moresubstrates at applicable design values of one or more processingvariables for the patterning process and then measured (e.g., using ascanning electron microscope) to derive the contour of the feature. Thiscontour obtained by measurement can then be designated as a nominalcontour. Additionally or alternatively, the feature can be created onone or more substrates at various different values of one or moreprocessing variables (e.g., one or more optical settings or conditionsas discussed above) and then measured (e.g., using a scanning electronmicroscope) to derive a plurality of contours of the feature, eachcontour at a different value of the one or more processing variables.These contours obtained by measurement can then be designated as nominalcontours with each nominal contour associated with a different value ofthe one or more processing variables. So, as a particular example, eachof the nominal contours can be associated with a different focus settingor condition (such as a certain variance from best focus).

So, in an embodiment, the nominal contour(s) can provide an indicationof the shape of the contour. For example, the nominal contour(s) canprovide an indication of the shape of the contour at a particular focuscondition. So, in the case of multiple nominal contours obtained aplurality of different focus conditions, each nominal contour canprovide an indication of the shape of the predicted contour at theapplicable focus condition.

Thus, in an embodiment and as will be discussed further, with nominalcontours that are each associated with a different value of one or moreprocessing variables (e.g., focus), the shape of a contour can bepredicted, for any value of the one or more processing variables, byreference to the nominal contours. Where a nominal contour is notavailable for a particular value of the one or more processingvariables, a contour can be generated by interpolation, extrapolation,etc. So, as an example, for any focus value on a certain location on asubstrate, the shape of the contour of the applicable pattern feature(s)of interest can be predicted.

So, at 1710, a first contribution/fingerprint can be obtained for theone or more processing variables for which the nominal contour(s) hasbeen determined. The first contribution/fingerprint can be obtainedusing any of the techniques described herein. In an embodiment, thefirst contribution/fingerprint corresponds to a situation prior to etch.

In an embodiment, the first contribution/fingerprint is of focus andthus, in an embodiment, the first contribution/fingerprint is an acrosssubstrate focus map. In an embodiment, the firstcontribution/fingerprint can be generated based on data obtained fromthe lithographic apparatus used to pattern the substrate. For example,the lithographic apparatus can provide focus information (e.g., focusresidual errors, etc.) and/or a characteristic of high frequency stagemovement (e.g., MSD) to construct the focus map. FIG. 14 shows anexample focus map 1800 for a patterning process, wherein differentshades schematically represent different variances from a nominal focus(e.g., best focus, an average focus, etc.).

At 1720, the first contribution/fingerprint 1710 is used to select anominal contour for a feature of interest. For example, at a particularlocation on the substrate and for a particular feature of interest, avalue for the one or more processing variables for which the nominalcontour(s) has been determined, can be determined from the firstcontribution/fingerprint 1710 and then used to select the associatednominal contour(s). Thus, in an example, where the firstcontribution/fingerprint 1710 is a focus map, the focus estimate at asubstrate location within the focus map can be used to obtain theassociated nominal contour as a prediction of the contour. Thus, apredicted contour can be determined per feature and per substratelocation.

Referring to FIG. 14 again, an example of such selection is depicted. InFIG. 14, nominal contours 1810, 1812, 1814 at best focus are shown. Now,at the location on the focus map 1800 associated with nominal contour1812, the focus map indicates that focus was at or near best focus.Accordingly, for that location, the nominal contour 1812 would beselected as a predicted contour. For the location associated withnominal contour 1810, the focus map indicates that focus was at anegative defocus −F. So, in that case, instead of using the nominalcontour 1810, a nominal contour determined for negative defocus −F,namely nominal contour 1820 would be selected. As seen in FIG. 14, thenominal contour 1820 has the characteristics of the feature but has adifferent shape due to negative defocus −F. Similarly, for the locationassociated with nominal contour 1814, the focus map indicates that focuswas at a positive defocus +F. So, in that case, instead of using thenominal contour 1814, a nominal contour determined for positive defocus+F, namely nominal contour 1830 would be selected. As seen in FIG. 14,the nominal contour 1830 has the characteristics of the feature but hasa different shape due to positive defocus +F. Thus, with a focus of −F,the nominal contour at best focus changes shape and similarly, with afocus of +F, the nominal contour at best focus changes shape. So, forexample, if F is variance from best focus and +F and −F have the sameabsolute value, then the respective contour shape changes may be thesame as shown in FIG. 14.

Referring back to FIG. 13, at 1730, a second contribution/fingerprintcan be obtained for one or more processing variables other than the oneor more processing variables for which the nominal contour(s) has beendetermined. The second contribution/fingerprint 1730 can be obtainedusing any of the techniques described herein. In an embodiment, thesecond contribution/fingerprint corresponds to a situation post-etch.

In an embodiment, the second contribution/fingerprint 1730 is ofcritical dimension and thus, in an embodiment, the secondcontribution/fingerprint is an across substrate critical dimension map(e.g., critical dimension uniformity map). In an embodiment, thecontribution/fingerprint can be generated based on data measured, usinga metrology tool, on one or more substrates having the pattern after theetching step of the patterning process. FIG. 15 shows an examplecritical dimension map 1900 for a patterning process, wherein differentshades schematically represent different variances from a nominalcritical dimension (e.g., design critical dimension, an average criticaldimension, etc.). So, for example, critical dimension map 1800 canrepresent critical dimension measured on an anchor aspect and plotted asa % of average critical dimension.

In an embodiment, the second contribution/fingerprint is corrected forthe impact of the one or more processing variables associated with thefirst contribution/fingerprint on the one or more processing variablesof the second contribution/fingerprint. So, for example, wherein thefirst contribution/fingerprint is a focus map and the secondcontribution/fingerprint is a critical dimension map, the secondcontribution/fingerprint can be corrected for the impact of focus (e.g.,the focus information (e.g., focus residual errors, etc.) and/or acharacteristic of high frequency stage movement)) on the criticaldimension in the second contribution/fingerprint. Details of determiningsuch an impact were described above. For example, a FEM can be used toisolate the focus impact on CD arising during the pattern transfer stepand then remove that impact from after-etch CD measurements.Additionally or alternatively, various lithographic apparatus signalscan be processed to arrive at an estimate of the focus during patterntransfer and its impact on CD and then remove that impact fromafter-etch CD measurements. As will be appreciated, the correction canbe made in various ways, including incorporating the correction directlyinto the second contribution/fingerprint, making a correction after avalue is selected from the second contribution/fingerprint as discussedbelow in relation to 1740, etc.

At 1740, the second contribution/fingerprint 1730 is used to modify anominal contour for a feature of interest. In an embodiment, the nominalcontour is the nominal contour selected at 1720. However, the selectionat 1720 could be skipped (but the modification performed) if a givennominal contour is already selected for the feature of interest withoutusing the selection step at 1720. Similarly, the modification at 1740could be skipped if a nominal contour is selected at step 1720 and itdoesn't require modification.

So, at 1740, for example, at a particular location on the substrate andfor a particular feature of interest, a value for the one or more otherprocessing variables is obtained from the secondcontribution/fingerprint 1730 and the value is then used to determine anappropriate modification of the nominal contour. In an embodiment, themodification is a change in size of the nominal contour. Thus, in anexample, where the second contribution/fingerprint 1730 is a criticaldimension map, the critical dimension estimate at a substrate locationwithin the critical dimension map can be used to modify the size of thenominal contour (e.g., the nominal contour selected at 1720) as aprediction of the contour. Thus, a predicted contour can be determinedper feature and per substrate location.

In an embodiment, a value of one or more other processing variablesobtained at a certain location from the second contribution/fingerprint1730 is assumed to apply to the entire feature of interest. So, if thecritical dimension of a feature represented in the secondcontribution/fingerprint 1730 deviates from a certain critical dimension(e.g., average critical dimension) by a certain amount (e.g., 5%), thenall critical dimensions of any feature at the same location will deviateby the same amount. Thus, this assumption means that a complete contouris resized by the same amount as the deviation in critical dimension.So, assuming a complete contour size of feature at a certain location onthe substrate changes relatively the same amount as the criticaldimension of an anchor aspect at the same location that has beenmeasured to obtain the second contribution/fingerprint 1730, then anominal contour can be shrunk by x % when critical dimension decreasesby x % and the nominal contour expands by x % when the criticaldimension increases by x %. The change is provided uniformly across thewhole contour.

Referring to FIG. 15 again, an example of such change in size isdepicted. In FIG. 15, nominal contours 1910, 1912, 1914 are shown. Now,at the location on the critical dimension map 1900 associated withnominal contour 1912 (which can be selected using step 1720), thecritical dimension map indicates that the critical dimension correspondsto a nominal critical dimension (e.g., design critical dimension, anaverage critical dimension, etc.) Accordingly, for that location, thenominal contour 1912 would be selected as a predicted contour. For thelocation associated with nominal contour 1910, the critical dimensionmap indicates that critical dimension was lower by a certain amount(e.g., −x %). So, in that case, instead of using the nominal contour1910, the nominal contour 1910 is shrunken by the certain amount (e.g.,−x %) to obtain predicted contour 1920. As seen in FIG. 15, the contour1920 has the characteristics of the feature but has a smaller size dueto the lower critical dimension. Similarly, for the location associatedwith nominal contour 1914, the critical dimension map indicates thatcritical dimension was higher by a certain amount (e.g., +x %). So, inthat case, instead of using the nominal contour 1914, the nominalcontour 1914 is increased in size by the certain amount (e.g., +x %) toobtain predicted contour 1930. As seen in FIG. 15, the contour 1930 hasthe characteristics of the feature but has a larger size due to thehigher critical dimension. Thus, with a critical dimension of −x %, thenominal contour is uniformly shrunken but still retains its shape, andwith a critical dimension of +x %, the nominal contour is uniformlyincreased in size but still retains its shape.

So, in an embodiment, given these two assumptions (namely that a valueof a certain one or more processing variables (e.g., focus) can predictcontour shape and a value of a certain one or more other processingvariables (e.g., CD) can predict contour size), a contour shape and sizecan be predicted for feature based on a value selected from one or morecontributions/fingerprints. In particular, for every location on asubstrate, the complete contours for one or more features of interestcan be predicted. In an embodiment, the feature of interest is adetermined hot spot.

In a particular embodiment, a contour is predicted from criticaldimension and focus measurements. In a particular embodiment, a contouris estimated using critical dimension and focus fingerprints.

At 1750, the predicted contour can be used in various applications. Forexample, the contour can be checked in of itself, or in relation to oneor more other contours, to determine whether a defect is predicted(e.g., there can be made one or more checks for necking, bridging, linepull back, line thinning, overlapping, resist top loss, and/or resistundercut). This technique can be useful in particular, for example, fordetermining bridging defects. These defects are caused by two featurestouching each other, which can in principle happen at any point on thecontours of two features (depending on the particular CD, focus, and/oroverlay conditions at that location). Use of contours enables morerobust evaluation of such defects compared with, e.g., evaluation ofdimensions at cut lines on the adjacent features.

As another example, the contour can be used to evaluate edge placementposition and/or error (which could also be used to identify a defectsuch as bridging). In effect, this technique can provide a computationalform of metrology to determine edge placement error. For example, with apredicted contour, a “virtual” edge placement error can be predicted.This can be used, for example, in multi-patterning defect predictionsthat are edge placement error driven. Thus, edge placement error drivendefects can be estimated using CD and focus fingerprints.

An example where the predicted contour can be used to determine apotential defect is in a spacer-and-cut layer process. An example ofthis is presented in FIGS. 16A-C. FIG. 16A depicts an examplespacer-and-cut layer process wherein lines 2000 are “cut” using apattern 2010. FIG. 16A depicts the nominal process where the lines 2000and pattern 2010 are at the desired alignment, size, etc. The result ofsuch a process would be a clean cut of the middle line 2000 by pattern2010. Now, the process of FIG. 13 can be applied using the maps 1800 and1900 shown schematically in FIG. 16 to arrive at a determination of thepredicted contours of lines 2000 and pattern 2010. In this example,shown in FIG. 16B, it is determined that the contour of pattern 2010 hasbeen predicted to increase in size (although in this example the shapehas not changed but it could have), while the predicted contours oflines 2000 are as expected. Now, FIG. 16C shows the result if thepredicted contour of pattern 2010 were used in the spacer-and-cut layerprocess. As seen at 2020, the pattern 2010 would undesirably cut aportion of the upper and lower lines 2000. Thus, in an embodiment, thepredicted operation of the spacer-and-cut layer process could be flaggedas producing a potential defect when pattern 2010 is used to cut lines2000.

As another example, the predicted contour can be used to determine apotential defect in a litho-etch litho-etch (LELE) process. An exampleof this is presented in FIGS. 17A-C. FIG. 17A depicts an examplelitho-etch and litho-etch process wherein lines 2100 are created in afirst litho-etch process and the pattern 2110 is interleaved with thelines 2100 through a second litho-etch process. FIG. 17A depicts thenominal process where the lines 2100 and pattern 2110 are at the desiredalignment, size, etc. The result of such a process would be a designedseparation between the pattern 2110 and the lines 2100. Now, the processof FIG. 13 can be applied using the maps 1800 and 1900 shownschematically in FIG. 17 to arrive at a determination of the predictedcontours of lines 2100 and pattern 2110. In this example, shown in FIG.17B, it is determined that the contour of pattern 2110 has beenpredicted to increase in size and change in shape, while the predictedcontours of lines 2100 are as expected. Now, FIG. 17C shows the resultif the predicted contour of pattern 2110 were used in the litho-etch andlitho-etch process. As seen at 2120, the pattern 2110 would undesirablybe too close to the lower line 2100 (e.g., the space between thefeatures is below a certain threshold); that is it be an overlap area orviolate a minimum distance requirement. This could result in a bridgingdefect. Further, the pattern 2110 could have a necking defect 2130 wherethe feature has changed in shape such that is has become too narrow(e.g., the width has gone below a threshold). Thus, in an embodiment,the predicted operation of the litho-etch and litho-etch process couldbe flagged as producing one or more potential defects when pattern 2110is created in conjunction with lines 2100. Thus, in an embodiment, fordefect prediction in a multiple exposure LELE type application, thepredicted contour should be able to improve the prediction capability ofnecking and/or bridging defects compared to using only defectindicators/cut-lines.

In another possible use of the predicted contour, the predict contourcan be used in model calibration, particularly calibration of an opticalproximity correction model. The predicted contour enables the correctionof etch fingerprints and/or focus fingerprints in measured gauges(contours). For example, this predicted contour can be used to calibratea mask data preparation after-etch model.

Thus, in an embodiment, this technique enables contour prediction from avirtual substrate; thus, the technique combines metrology withcomputation in order to generate contours without having to measurethem. In an embodiment, the technique enables prediction of variabilityin contours and edge placement error across a substrate, givenappropriate fingerprints (e.g., an after etch critical dimensionfingerprint and a lithographic apparatus focus fingerprint). In anembodiment, the technique enables better prediction capability formulti-patterning. In an embodiment, the technique enables patterncontrol by using edge placement optimization based on a predictedcontour.

In a further embodiment, the techniques described herein can be appliedto alignment measurement. As is known in the art, various alignmentmarks (e.g., in the form of diffraction gratings) are provided at leaston the substrate and the patterning device (e.g., mask). Alignment markscan also be provided on other structures, such as the substrate table.The alignment marks are measured with an alignment sensor to determinethe spatial position of one or more particular locations in a plane on asurface of the substrate and/or on the patterning device (including,e.g., a relative position between locations on the substrate and thepatterning device). The measured spatial positions are used tofacilitate proper positioning in, e.g., the X-Y plane of the transfer ofthe pattern onto the substrate, i.e., that the pattern is provided tothe proper location on the patterning receiving surface of thesubstrate.

Such proper positioning is particularly significant where a pattern hasbeen previously applied on the substrate and a subsequent pattern shouldbe aligned with that prior pattern; misalignment of patterns can becharacterized as an overlay error as described herein. To helpfacilitate proper alignment of a first device pattern with asubsequently applied second device pattern, an alignment mark for use inproper positioning of the second device pattern can be generated whenthe first device pattern is generated. For example, the patterningdevice pattern for generating the first device pattern can have one ormore alignment mark patterns that are transferred to the substrate whenthe first device pattern is transferred to the substrate. So, those oneor more alignment marks associated with the first device pattern areprocessed along with the first device pattern to generate an alignmentmark structure in a layer in the substrate associated with the firstdevice pattern. Then, when the second device pattern is desired to beapplied, those one or more alignment marks associated with the firstdevice pattern can be measured (often typically through one or morelayers, such as resist, applied over top) to determine the location of,e.g., the first device pattern so that a second device patternassociated with the first device pattern can be accurately placed.

An accurate alignment helps assure good overlay performance and therebyhigh yield in production. But space constraints on a substrate designedfor creating devices means that alignment marks cannot be providedeverywhere on that substrate (after all, the large majority of thatsubstrate should be used to apply patterns for generating devices).Further, time constraints limit the number of alignment marks perproduction substrate that can be measured during production whilemaintaining adequate throughput (e.g., number of production substratesprocessed per hour) of the manufacturing systems.

So, in a typical arrangement, a certain number of alignment marks aremeasured across the substrate (which will typically have a plurality ofdies/fields spread across the substrate where a pattern is transferredfrom the patterning device) to provide fairly good spatial coverageacross the substrate of the positions of locations on that substrate. Inan example scheme, a substrate alignment metrology sequence can measure20-100 alignment marks (locations) across the substrate. The result ofthose measurements captures a global fingerprint across the substratewith a relatively low spatial frequency per substrate. The measurementresults are used in conjunction with an alignment mathematical model.The aim of the model is to represent deviations between the transferredpositions of device pattern features compared with an ideal grid sothat, e.g., appropriate corrections by an apparatus in the devicemanufacturing process can be made based on the output of the model. Aswill be appreciated, more alignment marks than 20-100 can be providedacross the substrate but just 20-100 (e.g., 20-40) alignment marks aresampled due to, e.g., the throughput constraints. Further, all or alarge portion of these sampled alignment marks can be provided in areasnot usable for device patterns, e.g., in a scribe lane.

But this kind of relatively sparse sampling of alignment marks does notcapture a substrate fingerprint with high spatial frequency. As aresult, overlay performance may suffer.

In order to capture local effects (i.e., obtain a higher spatialfrequency), an intrafield alignment scheme can be used. But, it can haveone or more drawbacks. For example, relatively dense measurement ofalignment marks would need to be performed, which is likely not possibleto achieve without having an effect on throughput. Further, valuablein-die space would need to be occupied by alignment marks. And due toconstraints (such as throughput), intrafield alignment may be limited tofewer parameters than that which can be corrected by an apparatus (e.g.,the lithographic apparatus) in the device manufacturing process. Forexample, a model for intrafield alignment may be defined for 6parameters (e.g., magnification of the patterning device pattern (M),rotation about the z axis (R), translation in x and y (Cx, Cy),magnification in the y direction (My), and scan skew (RI)) per field,even though the lithographic apparatus may be capable of correctinghigher orders per device pattern transfer.

Thus, it would be desirable to have a denser alignment fingerprint,e.g., without having to perform more alignment mark measurements (suchas a dense intrafield alignment). So, using the techniques describedherein, a relatively dense alignment fingerprint (or a hybrid densealignment map (HDAM)) is computed by combining measured alignment datawith context information from relevant contributors to alignment. Thatis, as similarly described above in the context of other parameters suchas overlay and CD, a combination of fingerprints can be combined toobtain a derived fingerprint for alignment.

In particular, in production, local effects, such as substrate heightvariation due to, e.g., contamination, projection system aberration,patterning device writing error (i.e., the error in creating a patternon or by a patterning device such as an error in creating a pattern inan absorber layer of a mask), heating, process effects (such as chemicalmechanical planarization (CMP), etch, etc.), etc., could causedisplacement of at least part of an alignment mark (and of portions ofthe device pattern). One or more of those local effects can effectivelyhave a fingerprint with a relatively high spatial frequency, but whichmay not be captured by a typical alignment mark measurement sampling(which is constrained by, e.g., throughput and/or available die/fieldspace for alignment marks) used in production.

So, in an embodiment, the alignment contribution of one or more of theselocal effects is determined and combined with an alignment measurementat a relatively low density to yield a higher density alignmentfingerprint. The contributions to alignment of one or more of thevarious local effects can be derived from other metrology measurementsin the lithocell (e.g., in the lithographic apparatus) and/or becomputed/measured “offline” (that is, it need not be computed ormeasured during the processing of a particular substrate through thelithocell for which the HDAM is being determined).

So, FIG. 18 schematically shows an example of obtaining a derivedcontribution 2275 to alignment of a substrate, the derived contributionbeing a combination of contributions (one or more of which may be aderived contribution) of multiple processing parameters. So, the derivedcontribution 2275 can be obtained using the measured contribution froman alignment mark measurement 2200 combined with the contribution ofeach of one or more processing parameters (e.g., local effect processingparameters) such as substrate height 2205 due to, e.g., contamination,one or more process effects 2210 (such as chemical mechanicalplanarization (CMP), etch, etc.), heating 2215 (e.g., of the patterningdevice due to an illumination beam to obtain the patterned beam forexposure of the substrate), projection system aberration 2220, and/orpatterning device writing error 2225. Significantly, the processingparameter data can be obtained from the lithographic apparatus or otherpatterning process apparatus and can be a by-product of producing asubstrate as part of a patterning process. None of the contributionsassociated with these one or more processing parameters necessarilyrequires a measurement of an alignment mark on the substrate using analignment sensor.

So, in this alignment case, an example of the alignment fingerprint (A′)of an alignment mark measurement 2200 is shown as contribution 2240, anexample of the contribution to alignment of substrate height orunflatness (SH) 2205 is shown as contribution 2245 (the schematicdepiction shows substrate height data across a substrate which data canbe converted to a corresponding effect on alignment as describedherein), an example of the contribution to alignment of one or moreprocess effects (PE) 2210 (such as chemical mechanical planarization(CMP), etch, etc.) is shown as contribution 2250 (the schematicdepiction shows one or process effects data (such as etch effect data)across a substrate which data, if needed, can be converted to acorresponding effect on alignment as described herein), an example ofthe contribution to alignment of heating (RH) 2215 is shown ascontribution 2255 (the schematic depiction shows mask heating dataacross an exposure field of the mask which data can be converted to acorresponding effect on alignment at the substrate as described herein),an example of the contribution to alignment of projection systemaberration (PA) 2220 is shown as contribution 2260, and an example ofthe contribution to alignment of patterning device writing error (RWE)2225 is shown as contribution 2265. As will be appreciated, not all ofthese contributions 2245-2260 need to be combined with the contribution2240; rather, one or more contributions 2245-2260 can be combined withthe contribution 2240. The contributions can be obtained, as applicable,by simulation, mathematical modeling and/or measurement/experimentation.For example, the contributions can be obtained by simulation based onphysical models, empirical modeling and/or dedicated measurements.

Each of one or more of these contributions 2245-2260 can be combinedtogether 2270 with contribution 2240 to realize derived contribution2275. While element 2270 shows a plus sign, the operation at 2270 neednot be addition, e.g., it can be a multiplication, convolution, throughuse of a neural network etc. The operation may be different for one ormore contributions than another one or more contributions (e.g., anaddition of contribution 2245 and 2250 with contribution 2240 and aconvolution of the sum with one or more contributions 2255 to 2265). Inan example, the combined contribution to alignment can be expressed asA(x, y)=A′(x, y)+b₁*F(SH)(x, y)+c₁*F(PE)(x, y)+d₁*F(RH)(x,y)+e₁*F(PA)(x, y)+f₁*F(RWE)(x, y) . . . . The various functions can beobtained by simulation, mathematical modeling and/or experimentation.Moreover, there may be cross terms that are not shown here (such asfocus as a function of RH times PA, etc.).To obtain an absolute value ofalignment, a nominal value or simulated value of the alignment can becombined with the contributions. The coefficients such as b₁, c₁, etc.are sensitivities of the alignment with respect to the respectiveprocessing parameters or their functions. Some of the contributions areacross a substrate (e.g., process effects, substrate height orunflatness, etc.) but in an embodiment, one or more of the contributionsmay per die/field (which could then be repeated across the substratedepending on, e.g., applicable conditions at each of the instances) suchas the contributions of heating (RH) 2215, projection system aberration(PA) 2220, and patterning device writing error (RWE) 2225. As notedabove, the contribution 2275 may be characterized as a fingerprint sinceit can be spatially defined across the substrate/die/field. Further, thecontribution's translation into an absolute value may be characterizedas a fingerprint since it can be spatially defined across thesubstrate/die/field. As will be appreciated, data from processing ofmultiple substrates using the patterning process can be used to derivethe respective contributions. This data can already be available sinceit could be the by-product of processing the substrates.

Returning back to examples of processing parameters related to the localeffects, the contribution to alignment of substrate height or unflatness2205 can be a levelling substrate height map converted to an in-planedisplacement within the substrate (e.g., there can be more than 1000,more than 5000, more than 10,000, more than 20,000 or more than 50,000points per substrate and thus corresponding in-plane displacementscorresponding to an alignment contribution). The in-plane displacementsaffecting alignment and corresponding to a substrate height orunflatness can be obtained by simulation, mathematical modeling and/ormeasurement/experimentation. So, levelling measurements, which aresensitive to process induced contaminations, converted to in-planedisplacement can be used to refine and enrich alignment measurements toa higher density. In an embodiment, the levelling measurements are thosefor the state of the substrate when an alignment measurement is made.So, in embodiment, the fingerprint associated with substrate height orunflatness may be specific to the particular substrate underconsideration.

With particular technology, such as 3D-NAND, a levelling substrateheight map could particularly probe alignment displacement at theintrafield level (e.g., a higher amount of levelling points are used),after removing one or more process dependency artefacts. As is knownwith an optical level sensor, different substrates, and different partsof a substrate, will interact differently with the measurement beams ofradiation. In other words, the height measurements obtained by a levelsensor are subject to process-dependent effects and do not always givethe true height. In particular, an apparent surface depression is knownto be caused when light reflected from the substrate is subject toso-called Goos-Haenchen shift. This effect is different for differentmaterials and depends heavily on the structure and materials of severallayers. Therefore the apparent surface depression can vary significantlyfrom layer to layer, and between regions across the substrate. A heavilymetallized region will reflect light more reliably than a region withpredominantly dielectric material, for example. So, one or moretechniques, such as described U.S. Pat. No. 7,265,364, United StatesPatent Application Publication No. US 2010/0233600 and United StatesPatent Application Publication No. US 2016-0370711, incorporated hereintheir entireties by reference, can be used to correct for and/oridentify the one or process dependency artefacts for removal.

Another contribution due to a processing parameter related to a localeffect is a fingerprint associated with one or more process effects(e.g., an effect on alignment marks due to etch, CMP and/or one or moreother process steps) from processing other than the lithography patterntransfer step. Data of the one or more process effects can be determinedusing “offline” measurements using, e.g., a metrology apparatus asdepicted and described with respect to FIGS. 3-6. In an embodiment, thefingerprint of the one or more process effects can be a derivedcontribution determined as described above. The in-plane displacementsaffecting alignment corresponding to one or more process effects can beobtained by simulation, mathematical modeling and/ormeasurements/experimentation. In an embodiment, the process effect datais associated with the creation of the alignment mark prior to when analignment measurement is made for a particular lithography patterntransfer step based on that alignment mark. In an embodiment, thefingerprint associated with a process effect may not be dependent on theparticular substrate processed if the substrate(s) under considerationis subject to the same process effect. But, in some case, thefingerprint associated with a process effect may be specific to aparticular substrate where different substrates can be subject todifferent value of the process effect.

A further possible processing parameter is projection system aberration,which can induce a pattern shift. In an embodiment, the projectionsystem aberration can be measured in the lithographic apparatus using asensor (e.g., ASML's ILIAS sensor which is an interferometer typemeasurement apparatus used to measure aberrations and other parameters).In an embodiment, the projection system aberration for the alignmentmark pattern shift is computed based on an aberration residual measuredby a sensor. The in-plane displacements affecting alignmentcorresponding to the projection system aberration can be obtained bysimulation, mathematical modeling and/or measurements/experimentation.In an embodiment, the projection system aberration data is associatedwith the creation of the alignment mark prior to when an alignmentmeasurement is made for a particular lithography pattern transfer stepbased on that alignment mark. In an embodiment, the fingerprintassociated with projection system aberration can be determined for thedie/field and then repeatedly applied for one or more other dies/fieldsacross the substrate. Thus, the fingerprint associated with projectionsystem aberration may not be dependent on the particular substrateprocessed.

Heating is another possible processing parameter, which can induce apattern shift. In an embodiment, the heating is the heating of thepatterning device (e.g., mask) and/or the heating of the projectionsystem. In an embodiment, the heating is due to the extended exposure ofthe patterning device and/or projection system to illumination forpattern transfer. In an embodiment, the heating can be measured in thelithographic apparatus using a sensor (e.g., a temperature sensor). Inan embodiment, the heating can be calculated based on first principlesusing one or more patterning device and/or projection system properties(e.g., thermal materials characteristics) and illumination dose and/orcomputed based on mathematical model calibrated with appropriate dataderived from use of the lithographic apparatus. The in-planedisplacements affecting alignment corresponding to heating can beobtained by simulation, mathematical modeling and/ormeasurement/experimentation. In an embodiment, the heating is associatedwith the creation of the alignment mark prior to when an alignmentmeasurement is made for a particular lithography pattern transfer stepbased on that alignment mark. In an embodiment, the fingerprintassociated with heating can be determined for the die/field and thenrepeatedly applied for one or more other dies/fields across thesubstrate. Thus, the fingerprint associated with heating may not bedependent on the particular substrate processed.

Patterning device writing error is a further possible processingparameter, which can induce a pattern shift. In an embodiment, thepatterning device writing error is an error associated with forming thepattern in, or by, the patterning device itself. For example, a patternin an absorber of mask may not be perfectly created and thus thevariation from the designed pattern can be characterized as thepatterning device writing error. In an embodiment, the patterning devicewriting error can be obtained by “offline” measurements using ametrology apparatus. The in-plane displacements affecting alignmentcorresponding to patterning device writing error can be obtained bysimulation, mathematical modeling and/or measurement/experimentation. Inan embodiment, the patterning device writing error is associated withthe creation of the alignment mark prior to when an alignmentmeasurement is made for a particular lithography pattern transfer stepbased on that alignment mark. In an embodiment, the fingerprintassociated with patterning device writing error can be determined forthe die/field and then repeatedly applied for one or more otherdies/fields across the substrate. Thus, the fingerprint associated withpatterning device writing error may not be dependent on the particularsubstrate processed.

Information regarding one or more other possible processing parameters,when available, can also or alternatively be included such as servocontrol (moving average (MA) and/or moving standard deviation (MSD) inX, Y and/or Z), patterning device shape (e.g., a bending in the Zdirection), impact of a pellicle of patterning device, projection systemreference axis variation, etc. The corresponding in-plane displacementsaffecting alignment can be obtained by simulation, mathematical modelingand/or measurement/experimentation. In an embodiment, one or more of theprocessing parameters (e.g., patterning device shape, impact of apellicle, projection system reference axis, etc.) are associated withthe creation of the alignment mark prior to when an alignmentmeasurement is made for a particular lithography pattern transfer stepbased on that alignment mark. The information regarding these one ormore other possible processing parameters can be derived from metrologymeasurement in the lithographic apparatus (or the lithocell), derivedfrom “offline” metrology measurements, or determined by computation(e.g., simulation, calibrated mathematical model, first principles,etc.).

So, by combining alignment measurement data and an effect on alignmentdue to one or more processing parameters relating to local effects(which processing parameter data can be, e.g., lithographic apparatus orother lithocell metrology data and/or which can be process andapplication dependent), a hybrid dense alignment map (HDAM) can becomputed that is a pre-lithography pattern transfer output for, e.g.,control of the lithography pattern transfer. Since the hybrid densealignment map uses data obtained from separate sources, thiscomputational-based metrology can have an indication from the processand application's contribution separately.

A specific, non-limiting example work flow to compute a HDAM is shown inFIG. 19. That is, FIG. 19 schematically shows an example of deriving acombined contribution for alignment, wherein the example HDAM 2275 iscreated using the first 4 inputs listed in the example work flow of FIG.18. In this example, an alignment fingerprint 2240 of an alignment markmeasurement of a particular substrate under consideration is combinedwith three other contributions that are not obtained by alignmentmeasurement but rather converted into an effect on alignment asdescribed above to obtain a HDAM 2275. The other 3 inputs are thecontribution 2245 to alignment of substrate height or unflatness 2205(the schematic depiction shows substrate height data across a substratewhich data can be converted to a corresponding effect on alignment asdescribed herein), a contribution 2250 to alignment of one or moreprocess effects, such as chemical mechanical planarization (CMP), etch,etc. (the schematic depiction shows one or process effects data (such asetch effect data) across a substrate which data, if needed, can beconverted to a corresponding effect on alignment as described herein),and a contribution 2255 to alignment of patterning device heating (theschematic depiction shows patterning device heating data across anexposure field of the mask which data can be converted to acorresponding effect on alignment at the substrate as described hereinand which effect in the die/field can be repeated across the substrate).As will be appreciated, the various contributions can be re-griddedand/or scaled as appropriate to form the HDAM. Further, the density ofthe various contributions can be adjusted as desired to adjust theoverall density of the HDAM. So, by combining alignment data with analignment effect of one or more processing parameters, a computedalignment map can be created that is significantly denser than thealignment data alone.

The HDAM can be used for various purposes. An example use is as an inputto a control of the patterning process. For example, the HDAM can be aninput to control of the pattern transfer of the lithographic apparatus.In that respect, it can be used as an input for an interfield and/orintrafield substrate alignment model used for determining corrections ina lithographic apparatus. The combined dense alignment substrate mapprovides dense metrology information both at the interfield andintrafield level, and therefore could support usage of a high ordersubstrate alignment model as part of the control loop than where thealignment data is used alone.

Depending on the use case and input data, the alignment density can beenhanced as desired both at the interfield and intrafield level. Withsuch higher density metrology compared with a typical alignmenttechnique used in production, a high order interfield and/or intrafieldalignment model could have potentially higher accuracy for the modelcontent (if with a high order alignment model), which in turn improvesoverlay performance at the per substrate level. For example, FIG. 20schematically shows an example of how a patterning process correctedusing a fingerprint determined according to an existing alignmentmeasurement scheme translates to an overlay error fingerprint. Thealignment fingerprint 2240 is obtained using an existing alignmentmeasurement technique and used to correct the patterning process usingan alignment model. The overlay fingerprint of the corrected patterningprocess is shown as 2300. As can be seen in the fingerprint 2300, thereare quite a number of relatively high magnitude vectors showing thatthere are relatively significant overlay errors at various locationsacross the substrate. In comparison, FIG. 21 schematically shows anexample of how a patterning process corrected using a derivedfingerprint of alignment computed as described herein translates tooverlay error. The derived fingerprint or HDAM 2275 is obtained usingtechniques described herein and used to correct the patterning processusing an alignment model (which can be a higher order model than usedfor alignment fingerprint 2240 alone). In this example, the HDAM has asampling of about 1000 locations per substrate, which is significantlyhigher than using alignment measurement alone during production (giventhe time constraints of production) and is significantly denser withgreater on-device pattern coverage than using alignment measurementalone during production (given the in-die/field space constraints of theplacement of alignment marks). The overlay fingerprint of the correctedpatterning process is shown as 2310. As can be seen in the fingerprint2310, there are very few relatively high magnitude vectors showing thatthere are few relatively significant overlay errors at various locationsacross the substrate. Indeed, in an example, compared with an existingalignment technique, the overlay can be significantly improved (e.g.,overlay [mean plus three standard deviations] reduced from 4 nm to 1 nm)after high order corrections calculated from the output of the hybriddense alignment metrology are used.

In an embodiment, a contribution or the HDAM can be analyzed to identifya possible significant alignment error or residual (e.g., due to acontamination issue). This can be done by, e.g., statistical analysis ofthe data, by application of a threshold against the data or both. Ifthere is a significant alignment error, the metrology sampling can bere-distributed (e.g., increased, spatial concentrated, etc.) to enableimproved computational metrology input and/or refine the complexity ofthe modelling (e.g., provide a higher order model), with a desired to,e.g., avoid unnecessary rework of a substrate and so enable improvedoperation of the patterning process. As an example, in the case of adominant heating contribution at the substrate to substrate level, thiscomputational metrology can help by providing a high metrology densityat the intrafield level so that a higher order intrafield substratealignment model can be used, without a throughput hit and withoutsacrificing in die space.

So, there is provided, in an embodiment, a computational based alignmentmetrology that can construct a hybrid dense alignment map based on datafrom other than an alignment measurement (e.g., data from measurementsfrom other sensors in the patterning process such as data frommeasurements by a lithographic apparatus sensor other than the alignmentsensor). The HDAM can be produced “inline” and can be produced prior toa lithography pattern transfer step in which the HDAM can be used forcorrection; this can enable use of the HDAM data in, e.g., a feedforwardmanner and for corrections just prior to or during pattern transfer. Inan embodiment, the hybrid dense alignment map can be constructed basedon measurements from “offline” metrology (e.g., patterning devicewriting error, process effect (such as an effect of CMP, etch, etc.)which can be combined with “inline” metrology such as an alignmentmeasurement.

The computational based alignment metrology can construct a hybrid densealignment map that has increased density of a substrate alignmentfingerprint compared to just alignment measurement data and do so, e.g.,without causing a decline in substrate processing throughput and/orwithout sacrificing space within a substrate field/die. Thecomputational based alignment metrology can construct a hybrid densealignment map that enables higher order intrafield alignment based onthe hybrid dense alignment map compared to just alignment measurementdata. In an embodiment, one or more of the contributions to the hybriddense alignment map can be determined using a physical model, therebycan avoid model fitting. For example, a (offline) simulation or modelbased alignment fingerprint due to heating induced pattern shift can becalculated at the intrafield level, which can enable higher orderintrafield substrate alignment to compensate for a dominant displacementat the substrate to substrate level. As a further example, a (offline)simulation or model based alignment fingerprint due to opticalaberration induced pattern shift can be calculated to generate densemetrology data at the intrafield level, e.g., for usage of an intrafieldsubstrate alignment model. As another example, a (offline) simulation ormodel based alignment fingerprint due to patterning device writing errorinduced pattern shift can be calculated to generate dense metrology dataat the intrafield level, e.g., for usage of an intrafield substratealignment model. Measurements of heating, optical aberration and/orpatterning device writing error can be input to the determination of therespective alignment fingerprint.

An advantage of the HDAM is alignment metrology with a higher densitycompared with an existing alignment measurement process, which is ableto, e.g., capture a substrate fingerprint at a higher spatial frequencythan with the existing alignment measurement process. An additional oralternative advantage is that this computational metrology with multipleinputs (contributions) enables pre-lithography transfer clustering oferrors and a capability to include multiple automatic process controlthreads with, e.g., different priority in the patterning process. Anadditional or alternative advantage is that his computational metrologycan be performed “inline”, i.e., during processing of a substrate and socan be suitable for feedforward correction and/or as a tool foridentifying excursion of the process (so that the substrate can bereworked, scrapped, etc.). An additional or alternative advantage isthat this computational metrology can enable determination of a moreaccurate capture of a substrate fingerprint of alignment due to the highsampling density. An additional or alternative advantage is that thiscomputational metrology can enable improved overlay substrate tosubstrate performance due to a more accurate alignment input.

The results of the methods herein (or another result (e.g., a defectprediction) derived from the results of the methods herein) can be usedfor various purposes including control of a process in the patterningprocess or an apparatus therein, monitoring of substrates produced bythe patterning process, design of a process or apparatus of thepatterning process, etc. For example, the results or another resultderived therefrom can be used to alter an apparatus or process of thepatterning process for the further processing of the substrate or forthe processing of another substrate. For example, the results can beused to predict a defect. Prediction of a defect can be used, forexample, to control a metrology tool to inspect the affected area and/oralter an apparatus or process of the patterning process for the furtherprocessing of the substrate or for the processing of another substrate.Further, the results can be used to design the patterning process by,e.g., deriving a dose recipe for correction of the lithographicapparatus, enabling design of the patterning device and its pattern,setup of a process, etc. Further, the results can be used in modelcalibration, e.g., calibration of an optical proximity correction model,a source-mask optimization model, a lithographic manufacturing checkmodel, a resist model, an imaging model, a measurement model (e.g.,models the process of measuring), etc. The results can be used todetermine one or more variables of a process (e.g., best exposure and/orbest dose) which can then be used for various purposes. As will beappreciated, there can be many other uses.

In an embodiment, there is provided a method, comprising: determining afirst distribution of a first parameter associated with an error orresidual in performing a device manufacturing process; determining asecond distribution of a second parameter associated with an error orresidual in performing the device manufacturing process; anddetermining, by a hardware computer, a distribution of a parameter ofinterest associated with the device manufacturing process using afunction operating on the first and second distributions.

In an embodiment, the first parameter, the second parameter and theparameter of interest are the same. In an embodiment, the firstdistribution is specific to the device manufacturing process but notspecific to any particular substrate processed using the devicemanufacturing process. In an embodiment, the second distribution isspecific to a particular substrate processed using the devicemanufacturing process but not generic to other substrates processedusing the device manufacturing process. In an embodiment, the firstdistribution and/or second distribution comprises one or more selectedfrom: a contribution of a servo error to the respective first and/orsecond parameter, a contribution of alignment model residual to therespective first and/or second parameter, a contribution of a projectionsystem aberration or image plane deviation to the respective firstand/or second parameter, a contribution of a projection system modelresidual to the respective first and/or second parameter, and/or acontribution of a substrate surface height to the respective firstand/or second parameter. In an embodiment, determining the firstdistribution further comprises obtaining measured data of the firstparameter and removing therefrom a contribution of a particular deviceof the device manufacturing process to the first parameter. In anembodiment, the contribution of the particular device comprises one ormore selected from: a contribution of a servo error, a contribution ofalignment model residual, a contribution of a projection systemaberration or image plane deviation, a contribution of a projectionsystem model residual, and/or a contribution of a substrate surfaceheight. In an embodiment, the measured first parameter data comprisesfirst parameter data measured from a monitor substrate. In anembodiment, the first distribution, the second distribution and/or thedistribution of the parameter of interest comprises a spatial substratefingerprint. In an embodiment, the method further comprises using thedistribution of the parameter of interest to perform any one or moreselected from: predict a defect for a substrate, control the devicemanufacturing process, monitor the device manufacturing process, designan aspect of the device manufacturing process, and/or calibrate amathematical model. In an embodiment, the first parameter, the secondparameter and/or the parameter of interest is one or more selected from:overlay, CD, focus, dose, and/or edge position. In an embodiment, thedevice manufacturing process comprises a lithographic process and/or asemiconductor manufacturing process. In an embodiment, the functioncomprises one or more selected from: an arithmetic addition, aconvolution and/or a neural network. In an embodiment, the firstparameter and/or the second parameter is different than the parameter ofinterest and further comprising the first parameter and/or the secondparameter to the parameter of interest. In an embodiment, the methodfurther comprises determining the first distribution and/or the seconddistribution using data provided by a lithographic apparatus and/oretching apparatus used in the device manufacturing process.

In an embodiment, there is provided a method comprising: obtaining anunderlying contribution of a lithographic apparatus to overlay as partof a patterning process; and combining, by a hardware computer, theunderlying contribution with a further contribution to overlay of asubstrate to obtain an estimate of overlay for the substrate.

In an embodiment, the further contribution comprises a contribution of asubstrate surface height of the substrate to overlay. In an embodiment,the further contribution comprises a contribution of a substrate servoerror of the substrate to overlay. In an embodiment, the furthercontribution comprises a contribution of an alignment and/or projectionsystem model residual. In an embodiment, the method further comprisescombining, with the underlying contribution and the contribution of thesubstrate surface height, a contribution of an etch process to overlayof the substrate. In an embodiment, the etch process contribution isspecific to the patterning process but not specific to any particularsubstrate processed using the patterning process. In an embodiment, theunderlying contribution is specific to a particular patterning processbut not specific to any particular substrate processed using thepatterning process. In an embodiment, obtaining the underlyingcontribution further comprises obtaining measured overlay data andremoving therefrom a contribution of a particular component of thelithographic apparatus to overlay. In an embodiment, the contribution ofthe particular component comprises one or more selected from: acontribution of a servo error, a contribution of alignment modelresidual, a contribution of a projection system aberration, acontribution of a projection system model residual, and/or acontribution of a substrate surface height. In an embodiment, themeasured overlay data comprises overlay data measured from a monitorsubstrate. In an embodiment, the contribution comprises a spatialsubstrate fingerprint. In an embodiment, the method further comprisesusing the estimate to perform any one or more selected from: predict adefect for the substrate, control the patterning process, monitor thepatterning process, design an aspect of the patterning process, and/orcalibrate a mathematical model.

In an embodiment, there is provided a method, comprising: determining afirst distribution of measured alignment data in performing a devicemanufacturing process; determining a second distribution of alignmentdata derived from a processing parameter in the device manufacturingprocess; and determining, by a hardware computer system, a distributionof alignment data associated with the device manufacturing process as afunction of the first and second distributions.

In an embodiment, the processing parameter comprises one or moreselected from: a substrate height or unflatness, a process effect,optical element heating, optical aberration, and/or patterning devicewriting error. In an embodiment, the second distribution is derived froma plurality of processing parameters of the device manufacturingprocess. In an embodiment, the processing parameters comprise asubstrate height or unflatness, a process effect, and optical elementheating. In an embodiment, the second distribution is specific to thedevice manufacturing process but not specific to any particularsubstrate processed using the device manufacturing process. In anembodiment, the second distribution is specific to a particularsubstrate processed using the device manufacturing process but notgeneric to other substrates processed using the device manufacturingprocess. In an embodiment, the second distribution is derived from ameasurement of the processing parameter. In an embodiment, the methodfurther comprises using the distribution of alignment data to performany one or more selected from: predict a defect for a substrate, controlthe device manufacturing process, monitor the device manufacturingprocess, design an aspect of the device manufacturing process, and/orcalibrate a mathematical model. In an embodiment, the method furthercomprises altering a sampling of metrology data based on thedistribution of alignment data. In an embodiment, the method furthercomprises using a higher order alignment model with the distribution ofalignment data compared to that used with only the measured alignmentdata. In an embodiment, the method further comprises determining thefirst distribution and/or the second distribution using data provided bya lithographic apparatus used in the device manufacturing process. In anembodiment, the first distribution, the second distribution and/or thedistribution of the parameter of interest comprises a spatial substratefingerprint. In an embodiment, the device manufacturing processcomprises a lithographic process and/or a semiconductor manufacturingprocess. In an embodiment, the function comprises one or more selectedfrom: an arithmetic addition, a convolution and/or a neural network.

In an embodiment, there is provided a method comprising: obtaining analignment data distribution across at least part of a substrateprocessed using a patterning process, based on measured alignment data;and combining, by a hardware computer, the alignment data distributionwith an alignment fingerprint attributable to a processing parameterother than measured alignment to obtain an estimate of alignment datafor the substrate.

In an embodiment, the alignment fingerprint comprises a contribution ofa substrate height or unflatness of the substrate to alignment. In anembodiment, the alignment fingerprint comprises a contribution of aprocess effect, due to a part of the patterning process other than alithography pattern transfer, of the substrate to alignment. In anembodiment, the alignment fingerprint comprises a contribution ofheating of the substrate to alignment. In an embodiment, the alignmentfingerprint is specific to the patterning process but not specific toany particular substrate processed using the patterning process. In anembodiment, the alignment fingerprint is specific to a particularsubstrate processed using the patterning process but not generic toother substrates processed using the patterning process. In anembodiment, the alignment fingerprint is derived from a measurement ofthe processing parameter. In an embodiment, the alignment fingerprintcomprises a spatial substrate fingerprint. In an embodiment, the methodfurther comprises using the estimate to perform any one or more selectedfrom: predict a defect for the substrate, control the patterningprocess, monitor the patterning process, design an aspect of thepatterning process, and/or calibrate a mathematical model.

Input contributors for computational metrology (CM) of overlay may bemeasurements collected by exposure sensors of a scanner and inspectiontools. For instance, they may include level sensor and alignment sensormeasurements, stage dynamic servo logging, overlay and other offlinemetrology measurements.

If we take alignment input as an example contributor, a high-orderalignment model, e.g. based on a 3rd order polynomial, is used tocalculate model content from alignment measurements. Such model contentmay be dominated by a wafer deformation contribution together withalignment mark deformation. But for accurate overlay metrologymonitoring, control or defect prediction, only the wafer deformationcontribution is a true signal. Alignment mark deformation is notrelevant and is a source of error (or ‘noise’) that should be excluded.The consequence of including such incorrect model content isinconsistent performance of computational metrology (CM). For waferssuffering only from minor alignment mark deformation, alignment inputwith a high-order model can improve the metrology accuracy due to highersignal-to-noise ratio. For wafers suffering from severe alignment markdeformation, this input can degrade metrology accuracy due to lowsignal-to-noise ratio. The error (or ‘noise’) is proportional to theorder of the model being used. Typically, it occurs at locations, e.g.at wafer edges, where alignment marks deform the most due toprocess-induced effects. Such limitations leads to a lower-order modelbeing chosen to limit the amplitude of the ‘noise’, but then performanceof CM is limited because the true wafer deformation signal, which isonly captured by the high-order model, is missing from the input.

Note that these limitations generally exist for other inputcontributors, e.g. level sensor measured wafer height map, scannerdynamics, offline metrology measured etching induced overlay, bottomgrating asymmetry measurement, CD measurement, etc.

When including measurements from scanners or offline metrology as inputcontributors to CM, the orthogonality between the contributors is auseful assumption. With this assumption, the contributors can be addedand correlated without cross talk with the parameters of interest, e.g.patterning process parameters such as after-develop overlay, after-etchoverlay, or SEM-measured CD or overlay. However, these contributors maystill interfere with each other, particularly at specific spatialfrequency conditions. Depending on the parameters of interest, thesecontributors can also correlate with the parameters of interest atdifferent conditions.

In a frequency distribution of multiple input contributors for CM, at ahigh (>100 Hz) frequency range, scanner metrology input (e.g. levelsensors that measure wafer height map) may predict overlay content withminor crosstalk from other contributors (e.g. scanner dynamics servoerror).

However, at a low (<100 Hz) frequency range, contributors share commonfrequency windows. These contributors include for example, waferalignment model content, monitor wafer model content, level sensormeasurement, dynamic servo data. This implies that such model contentcould interfere with each other. But also it indicates that thesecontributors could correlate with a specific part of overlay content fora particular frequency condition, here called a frequency window. Forthe signal outside of these frequency windows, unwanted contributionsmay become part of ‘noise’ and may decrease the accuracy of the CM.Therefore, it would be advantageous to exclude such ‘noise’ from theinput contributors of CM, via for instance frequency low/high/band passfilters, to increase the signal-to-noise ratio. Embodiments describedbelow provide a methodology for CM to exclude such “noise”.

Such functionality is also useful to calibrate the outcome of CM fordifferent parameters of interest for generalized data usage of otherapplications. For instance, between optically-measured overlay andSEM-measured device feature dependent overlay, targets responddifferently to patterning processing due to different dimensions anddesign. Such functionality is useful to exclude the un-correlatedoverlay content between optically-measured contributors and the responseof features of actual devices, from a defect prediction point of view.

In an embodiment, a model or NCE (non-correctable error) model may actas a frequency low/high pass filter, and a set of specific modelparameters can act as a frequency band pass filter. This means as longas pairs of specific model parameters deduced from any of the two inputdata (i.e. contributors or any patterning process parameters) showcorrelation within each pair, weights between the two input data, hereincalled calibration factors, can be determined accordingly.

In an embodiment, a methodology is provided to deduce the calibrationfactors for the correlating model parameters between any of the twoinput contributors or parameters of interest. To aid understanding, wedescribe the methodology in terms of predicting one domain from anotherother domain. The input contributor used for a prediction are defined asDomain A. The parameter of interest is defined as Domain B.

The input contributor Domain A may be processing variables as describedwith reference to FIG. 7, such as alignment variables. The parameter ofinterest Domain B may be a patterning process parameter as describedwith reference to FIGS. 7 and 8, such as overlay.

FIG. 22 schematically shows a flow for a method, according to anembodiment.

The parameter of interest distribution 2322 (DB), such as an overlaydistribution, is determined. This is the first distribution 2322 of afirst parameter 2321 associated with an error or residual in performinga device manufacturing process. To determine the distribution 2322, afirst distribution of values 2325 of the first parameter 2321 isobtained. The first distribution of values 2325 is then modeled 2328 toobtain the first modeled distribution of values 2322 (DB). Thus, in thisembodiment, the determined first distribution (parameter of interest)comprises a first modeled distribution of values 2322 (DB).

An input contributor distribution 2312 (DA), such as an alignmentdistribution, is determined. This is the second distribution 2312 of afirst parameter 2311 associated with an error or residual in performinga device manufacturing process. To determine the distribution, a seconddistribution of values 2315 of the first parameter 2311 is obtained. Thefirst distribution of values 2315 is then modeled 2318 to obtain thesecond modeled distribution of values 2312 (DA). Thus, in thisembodiment, the determined second distribution (input contributor)comprises a first modeled distribution of values 2312 (DA).

For the modelling 2328, 2318, a scale of variation 2304 (SV) (e.g.frequency <100 Hz) is determined 2302 for which a correlation betweenvalues of the first distribution 2325 and values of the seconddistribution 2315 exceeds a threshold. The first and second distributionof values are then modeled 2328, 2318 in dependence of the determinedscale of variation 2304 (SV) to obtain the first modeled distributionand second modeled distribution of values 2322 (DB), 2312 (DA).

Next, a distribution of the parameter of interest (which, in thisembodiment, is the first parameter, e.g. overlay) is determined, by ahardware computer, using a function operating on the first and seconddistributions 2322 (DB), 2312 (DA). The function in this embodimentcomprises a correlation 2332 (CORR) operating on the first and seconddistributions 2322, 2312.

Determination of the distribution of the parameter of interest 2352(DB′) is based on scaling 2335 the modeled second distribution 2312 (DA)using a scaling factor 2334 (Calibration Factor CF) obtained by mapping2332 (CORR) between the first model coefficient associated with thefirst modeled distribution of values 2322 (DB) and the second modelcoefficient associated with the second modeled distribution of values2312 (DA). The scaling factor 2334 (Calibration Factor, CF) may be usedto exclude a modeled component from the step of determining thedistribution of the parameter of interest 2352. For example, if thescaling factor is below or equal to a threshold 2333, then a modelcoefficient associated with the first modeled distribution of values2312 (DA) may be excluded from the scaling.

FIGS. 23 and 24 schematically shows adjusting calibration factors topredict a distribution of a parameter of interest. A correlation betweentwo domains Domain A (alignment) and Domain B (overlay) may be defined.For two domains which can be described by the same set of parameters,e.g. linear, high-order or combined polynomial coefficients, a set ofscaling factors or calibration factors can be defined for thecorrelating coefficients, by dividing a coefficient of Domain B with acoefficient of Domain A using simple linear algebra.

In the case of one domain receiving correction from the other domain,there is a high probability of good correlation existing between thesetwo domains, with a large number of data points given. For example, ascanner corrects a substrate grid (deformation) using information froman alignment measurement. There is an assumption that there is a strongcorrelation between alignment and overlay for parameters up to 5^(th)order polynomial components used within an alignment model. In otherwords, Domain B (overlay) receives correction from Domain A (alignment)and there is a strong correlation between Domain A and Domain B.

FIGS. 23 and 24 illustrate predicting one domain DB′ by projecting theother domain DA with calibration factors for all model parameters.First, all model parameters are calculated for each domain. Two modelparameters MPA and MPB each have eight of their points P1 to P8tabulated.

With respect to FIG. 23, table 2362 shows values of MPA for Domain A(DA) and Domain B (DB). Graph 2366 is a plot of MPA for Domain A versusMPA for Domain B, including the data points in table 2362. Correlationis determined by fitting a linear model (y=a*x) to determine acalibration factor between the sets of parameters for the modelparameter MPA, here 0.50 (y=0.5*x).

With respect to FIG. 24, table 2364 shows values of MPB for Domain A(DA) and Domain B (DB). Graph 2368 is a plot of MPB for Domain A versusMPB for Domain B, including the data points in table 2364. Correlationis determined by fitting a linear model (y=a*x) to determine acalibration factor between the sets of parameters for the modelparameter MPB, here 0.33 (y=0.33*x).

The calibration factors are used to predict the model parameters of theparameter of interest DB′ (e.g. overlay) from the Domain A parametervalues, as shown in tables 2370 in FIGS. 23 and 2372 in FIG. 24, formodel parameters MPA and MPB respectively.

Even though there may be a perfect correlation between Domain A andDomain B, it does not guarantee that the weights between two set ofparameters are 1. For instance, a wafer-to-wafer translation value of analignment measurement can be two times bigger than that of a translationobserved in the context of the overlay error. In this case, even thoughthere are perfect correlations between two set of parameters, scales arenot always 1. In other words, if there are strong correlations betweentwo set of parameters, Domain B can be more precisely predicted byadjusting the calibration factor for the parameters which are to bemultiplied with those of Domain A. Note that to have a good quality ofprediction, the input sampling of Domain A and Domain B preferably is tobe constrained to avoid cross-talk between model parameters due toasymmetric layout of input sampling.

If alignment and overlay correlate with scale 1, it means that overlaycorrection is based on information representative of real waferdeformation. in this case alignment information which is true and real.In this case, the calibration factors from two sets of parameters areall 1 which is same as the observed scale.

If alignment measurement suffers from alignment mark asymmetry ormetrology measurement uncertainty, it means that for the alignment,there is false information coming from deformed alignment marks. If thealignment model is calculated with this false information, such errorsinduced from mark deformation will be dialed into overlay prediction. Inan embodiment, by only looking at those correlated model parametersbetween alignment and overlay for which correlation is good enough, acalibration factor between alignment and overlay can be calculated perparameter. By applying these selected calibration factors to thealignment data, overlay prediction induced by false alignment markdeformation can be calibrated (filtered) for all parameters.

Due to the deformation of metrology overlay targets, usually there is anoffset between metrology target overlay and device overlay. This offsetbudget can be separated into ‘batch’ and ‘wafer-to-wafer’ (W2W)categories. While ‘batch’ offset is calculated based on real deviceoverlay measurement, in case of W2W, if there is a stable correlationbetween metrology and device overlays, calibration factors can bedefined and used to calibrate/predict this offset as W2W in the waydescribed above. This can be understood by replacing Domain A with‘metrology overlay’ and Domain B with ‘device overlay’.

Calibration/prediction of overlay maybe extended using contextinformation; using the concept of context-based grouping. For the casewhere production lots are split into a few groups and each group isprocessed separately with different process tools, the fingerprint ofeach group (or degree of wafer/mark deformation/asymmetry) would bedifferent from each other. In this case, the total dataset can begrouped into sub-datasets and correlation/calibration factor can becalculated again per group. The calibration/prediction calculated wouldbe applied to each group separately leading bettercalibration/prediction results.

FIG. 25 schematically shows the determination of the possibility ofcorrect prediction. The vertical axis DB is Domain B model parametervalue and the horizontal axis DA is Domain A model parameter value.

While calculating the calibration factor for each dataset, a possibilityof correct prediction can be defined using the framework as describedbelow, with an assumption that data points are distributed evenly.

(1) If a certain data point is in the region 2704 between the slope ofthe correlation factor line 2706 and axis of Domain B (DB), thepredicted value is always bigger than zero and less than the value ofDomain B. Then, a certain portion of Domain B can be projected/predictedcorrectly.

(2) If a data point is exactly on the slope 2706, projection/predictionare perfect.

(3) If a point is in the region 2708 between slope 2706 and half of theslope 2710, prediction is possible. But the prediction value is largerthan the value of Domain B. Calibration to this data point changes thesign of the calibrated result.

(4) For data points located in other regions than these three (2704,2706 and 2708) calibration of Domain B using the method described hereinmakes the result worse than original value.

With this, an area of correct prediction can be defined below with theangle θ between the axis Domain A axis and the slope 2706. As the slopebecomes closer to the x-axis, the possibility of correctprojection/prediction becomes its maximum value of 50%, at the angle ofθ₁. But the benefit of using this projection becomes closer to zero asthe calibration factor is close to zero. Therefore, finding a specificfrequency window or conditions with good correlation between the twodomains is very important (e.g. using separation of the total datasetinto subsets). This will make a distribution of data points which isconcentrated on the slope which would be within the three regions (2704,2706 and 2708) explained above. Also, a trade-off between calibrationfactor and correction possibility is possible. Calibration factors whichare defined during a correlating (setup) phase may be adjusted to besmaller than their originally defined values. This will increase thenumber of data points correctly predicted/calibrated, but the benefitwill be smaller than it would have been.

The calibration factor (F_(cal))=tan (θ). The predictionpossibility=area of arc divided by that of circle with infinite radius

$= {\frac{1}{2} - {\frac{1}{\pi}{( {\tan^{- 1}\frac{F_{cal}}{2}} ).}}}$

Embodiments provide a generalized methodology to determine calibrationfactors between filtered frequencies, here called correlating modelparameters, from any of the domains and to project one domain to theother domain for metrology prediction/calibration purposes, with thecapability to correct domain projection with respect to the value of acalibration factor.

Embodiments are capable of calibrating overlay prediction from waferdeformation/alignment mark asymmetry with domain projection, across themultiple wavelengths (colors) in sensors, multi-reference measurementsin time (wafers) and multiple spatial frequencies within the measurement(locations).

Embodiments separate the data into subsets increasing correlationbetween two domains and prediction accuracy.

Embodiments are capable of de-selecting the content from un-correlatingmodel parameters of both domains, to suppress the noise of predictioninduced from input contributors.

Embodiments are capable of providing indications of wafers needing realproduction measurement. For example, if measured scanner metrology froma new Domain A does not fall into the previously observed population anymore, actions can be triggered to measure the actual wafer in Domain Bto update the previously defined population.

Embodiments calibrate out a portion of false content measured by scanneror any overlay metrology from prediction, i.e., alignment markasymmetry, mis-corrected wafer deformation, or any un-correlatingcontent within the input contributors.

Embodiments can be used for any of the input data and parameters ofinterest, i.e. offline wafer shape measurement or SEM measurement.

For wafer-to-wafer variation feedforward, embodiments are able topredict wafer-to-wafer corrections for a subsequent layer from aprevious layer's alignment when there is a correlation between thesetwo. For example, for a layer that has had Litho-Etch-Litho-Etchprocessing.

FIG. 26 is a block diagram that illustrates a computer system 100 whichcan assist in implementing methods and flows disclosed herein. Computersystem 100 includes a bus 102 or other communication mechanism forcommunicating information, and a processor 104 (or multiple processors104 and 105) coupled with bus 102 for processing information. Computersystem 100 also includes a main memory 106, such as a random accessmemory (RAM) or other dynamic storage device, coupled to bus 102 forstoring information and instructions to be executed by processor 104.Main memory 106 also may be used for storing temporary variables orother intermediate information during execution of instructions to beexecuted by processor 104. Computer system 100 further includes a readonly memory (ROM) 108 or other static storage device coupled to bus 102for storing static information and instructions for processor 104. Astorage device 110, such as a magnetic disk or optical disk, is providedand coupled to bus 102 for storing information and instructions.

Computer system 100 may be coupled via bus 102 to a display 112, such asa cathode ray tube (CRT) or flat panel or touch panel display fordisplaying information to a computer user. An input device 114,including alphanumeric and other keys, is coupled to bus 102 forcommunicating information and command selections to processor 104.Another type of user input device is cursor control 116, such as amouse, a trackball, or cursor direction keys for communicating directioninformation and command selections to processor 104 and for controllingcursor movement on display 112. This input device typically has twodegrees of freedom in two axes, a first axis (e.g., x) and a second axis(e.g., y), that allows the device to specify positions in a plane. Atouch panel (screen) display may also be used as an input device.

According to one embodiment, portions of the process may be performed bycomputer system 100 in response to processor 104 executing one or moresequences of one or more instructions contained in main memory 106. Suchinstructions may be read into main memory 106 from anothercomputer-readable medium, such as storage device 110. Execution of thesequences of instructions contained in main memory 106 causes processor104 to perform the process steps described herein. One or moreprocessors in a multi-processing arrangement may also be employed toexecute the sequences of instructions contained in main memory 106. Inan alternative embodiment, hard-wired circuitry may be used in place ofor in combination with software instructions. Thus, the descriptionherein is not limited to any specific combination of hardware circuitryand software.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 104 forexecution. Such a medium may take many forms, including but not limitedto, non-volatile media, volatile media, and transmission media.Non-volatile media include, for example, optical or magnetic disks, suchas storage device 110. Volatile media include dynamic memory, such asmain memory 106. Transmission media include coaxial cables, copper wireand fiber optics, including the wires that comprise bus 102.Transmission media can also take the form of acoustic or light waves,such as those generated during radio frequency (RF) and infrared (IR)data communications. Common forms of computer-readable media include,for example, a floppy disk, a flexible disk, hard disk, magnetic tape,any other magnetic medium, a CD-ROM, DVD, any other optical medium,punch cards, paper tape, any other physical medium with patterns ofholes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip orcartridge, a carrier wave as described hereinafter, or any other mediumfrom which a computer can read.

Various forms of computer readable media may be involved in carrying oneor more sequences of one or more instructions to processor 104 forexecution. For example, the instructions may initially be borne on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 100 canreceive the data on the telephone line and use an infrared transmitterto convert the data to an infrared signal. An infrared detector coupledto bus 102 can receive the data carried in the infrared signal and placethe data on bus 102. Bus 102 carries the data to main memory 106, fromwhich processor 104 retrieves and executes the instructions. Theinstructions received by main memory 106 may optionally be stored onstorage device 110 either before or after execution by processor 104.

Computer system 100 also preferably includes a communication interface118 coupled to bus 102. Communication interface 118 provides a two-waydata communication coupling to a network link 120 that is connected to alocal network 122. For example, communication interface 118 may be anintegrated services digital network (ISDN) card or a modem to provide adata communication connection to a corresponding type of telephone line.As another example, communication interface 118 may be a local areanetwork (LAN) card to provide a data communication connection to acompatible LAN. Wireless links may also be implemented. In any suchimplementation, communication interface 118 sends and receiveselectrical, electromagnetic or optical signals that carry digital datastreams representing various types of information.

Network link 120 typically provides data communication through one ormore networks to other data devices. For example, network link 120 mayprovide a connection through local network 122 to a host computer 124 orto data equipment operated by an Internet Service Provider (ISP) 126.ISP 126 in turn provides data communication services through theworldwide packet data communication network, now commonly referred to asthe “Internet” 128. Local network 122 and Internet 128 both useelectrical, electromagnetic or optical signals that carry digital datastreams. The signals through the various networks and the signals onnetwork link 120 and through communication interface 118, which carrythe digital data to and from computer system 100, are example forms ofcarrier waves transporting the information.

Computer system 100 can send messages and receive data, includingprogram code, through the network(s), network link 120, andcommunication interface 118. In the Internet example, a server 130 mighttransmit a requested code for an application program through Internet128, ISP 126, local network 122 and communication interface 118. Onesuch downloaded application may provide for the illuminationoptimization of the embodiment, for example. The received code may beexecuted by processor 104 as it is received, and/or stored in storagedevice 110, or other non-volatile storage for later execution. In thismanner, computer system 100 may obtain application code in the form of acarrier wave.

Further embodiments are disclosed in the list of numbered embodimentsbelow:

-   1. A method, comprising:

determining a first distribution of a first parameter associated with anerror or residual in performing a device manufacturing process;

determining a second distribution of a second parameter associated withan error or residual in performing the device manufacturing process; and

determining, by a hardware computer, a distribution of a parameter ofinterest associated with the device manufacturing process using afunction operating on the first and second distributions.

-   2. The method of embodiment 1, wherein the first parameter, the    second parameter and the parameter of interest are the same.-   3. The method of embodiment 1, wherein the first distribution is    specific to the device manufacturing process but not specific to any    particular substrate processed using the device manufacturing    process.-   4. The method of embodiment 1, wherein the second distribution is    specific to a particular substrate processed using the device    manufacturing process but not generic to other substrates processed    using the device manufacturing process.-   5. The method of embodiment 1, wherein the first distribution and/or    second distribution comprises one or more selected from: a    contribution of a servo error to the respective first and/or second    parameter, a contribution of alignment model residual to the    respective first and/or second parameter, a contribution of a    projection system aberration or image plane deviation to the    respective first and/or second parameter, a contribution of a    projection system model residual to the respective first and/or    second parameter, and/or a contribution of a substrate surface    height to the respective first and/or second parameter.-   6. The method of embodiment 1, wherein determining the first    distribution further comprises obtaining measured data of the first    parameter and removing therefrom a contribution of a particular    device of the device manufacturing process to the first parameter.-   7. The method of embodiment 6, wherein the contribution of the    particular device comprises one or more selected from: a    contribution of a servo error, a contribution of alignment model    residual, a contribution of a projection system aberration or image    plane deviation, a contribution of a projection system model    residual, and/or a contribution of a substrate surface height.-   8. The method of embodiment 6, wherein the measured first parameter    data comprises first parameter data measured from a monitor    substrate.-   9. The method of embodiment 1, wherein the first distribution, the    second distribution and/or the distribution of the parameter of    interest comprises a spatial substrate fingerprint.-   10. The method of embodiment 1, further comprising using the    distribution of the parameter of interest to perform any one or more    selected from: predict a defect for a substrate, control the device    manufacturing process, monitor the device manufacturing process,    design an aspect of the device manufacturing process, and/or    calibrate a mathematical model.-   11. The method of embodiment 1, wherein the first parameter, the    second parameter and/or the parameter of interest is one or more    selected from: overlay, CD, focus, dose, and/or edge position.-   12. The method of embodiment 1, wherein the device manufacturing    process comprises a lithographic process and/or a semiconductor    manufacturing process.-   13. The method of embodiment 1, wherein the function comprises one    or more selected from: an arithmetic addition, a convolution and/or    a neural network.-   14. The method of embodiment 1, wherein the first parameter and/or    the second parameter is different than the parameter of interest and    further comprising converting the first parameter and/or the second    parameter to the parameter of interest.-   15. The method of embodiment 1, further comprising determining the    first distribution and/or the second distribution using data    provided by a lithographic apparatus and/or etching apparatus used    in the device manufacturing process.-   16. The method of embodiment 1, wherein the function comprises a    correlation operating on the first and second distributions.-   17. The method of embodiment 16, wherein:

the determined first distribution comprises a first modeled distributionof values; and

the determined second distribution comprises a second modeleddistribution of values; and

the parameter of interest is the first parameter,

and the method comprises:

obtaining a first distribution of values of the first parameter;

obtaining a second distribution of values of the second parameter;

modeling the first and second distribution of values to obtain the firstmodeled and second modeled distribution of values; and

determining the distribution of the parameter of interest based onscaling the modeled second distribution using a scaling factor obtainedby mapping between a first model coefficient associated with the firstmodeled distribution of values and a second model coefficient associatedwith the second modeled distribution of values.

-   18. The method of embodiment 17, comprising:

determining a scale of variation for which a correlation between valuesof the first distribution and values of the second distribution exceedsa threshold; and

modeling the first and second distribution of values in dependence ofthe determined scale of variation to obtain the first modeled and secondmodeled distribution of values.

-   19. The method of embodiment 17, comprising using the scaling factor    to exclude a modeled component from the step of determining the    distribution of the parameter of interest.-   20. A method comprising:

obtaining an underlying contribution of a lithographic apparatus tooverlay as part of a patterning process; and

combining, by a hardware computer, the underlying contribution with afurther contribution to overlay of a substrate to obtain an estimate ofoverlay for the substrate.

-   21. The method of embodiment 20, wherein the further contribution    comprises a contribution of a substrate surface height of the    substrate to overlay.-   22. The method of embodiment 20, wherein the further contribution    comprises a contribution of a substrate servo error of the substrate    to overlay.-   23. The method of embodiment 20, wherein the further contribution    comprises a contribution of an alignment and/or projection system    model residual.-   24. The method of embodiment 20, further comprising combining, with    the underlying contribution and the contribution of the substrate    surface height, a contribution of an etch process to overlay of the    substrate.-   25. The method of embodiment 24, wherein the etch process    contribution is specific to the patterning process but not specific    to any particular substrate processed using the patterning process.-   26. The method of embodiment 20, wherein the underlying contribution    is specific to a particular patterning process but not specific to    any particular substrate processed using the patterning process.-   27. The method of embodiment 20, wherein obtaining the underlying    contribution further comprises obtaining measured overlay data and    removing therefrom a contribution of a particular component of the    lithographic apparatus to overlay.-   28. The method of embodiment 27, wherein the contribution of the    particular component comprises one or more selected from: a    contribution of a servo error, a contribution of alignment model    residual, a contribution of a projection system aberration, a    contribution of a projection system model residual, and/or a    contribution of a substrate surface height.-   29. The method of embodiment 27, wherein the measured overlay data    comprises overlay data measured from a monitor substrate.-   30. The method of embodiment 20, wherein the contribution comprises    a spatial substrate fingerprint.-   31. The method of embodiment 20, further comprising using the    estimate to perform any one or more selected from: predict a defect    for the substrate, control the patterning process, monitor the    patterning process, design an aspect of the patterning process,    and/or calibrate a mathematical model.-   32. A method, comprising:

determining a first distribution of measured alignment data inperforming a device manufacturing process;

determining a second distribution of alignment data derived from aprocessing parameter in the device manufacturing process; and

determining, by a hardware computer system, a distribution of alignmentdata associated with the device manufacturing process as a function ofthe first and second distributions.

-   33. The method of embodiment 32, wherein the processing parameter    comprises one or more selected from: a substrate height or    unflatness, a process effect, optical element heating, optical    aberration, and/or patterning device writing error.-   34. The method of embodiment 32, wherein the second distribution is    derived from a plurality of processing parameters of the device    manufacturing process.-   35. The method of embodiment 34, wherein the processing parameters    comprise a substrate height or unflatness, a process effect, and    optical element heating.-   36. The method of embodiment 32, wherein the second distribution is    specific to the device manufacturing process but not specific to any    particular substrate processed using the device manufacturing    process.-   37. The method of embodiment 32, wherein the second distribution is    specific to a particular substrate processed using the device    manufacturing process but not generic to other substrates processed    using the device manufacturing process.-   38. The method of embodiment 32, wherein the second distribution is    derived from a measurement of the processing parameter.-   39. The method of embodiment 32, further comprising using the    distribution of alignment data to perform any one or more selected    from: predict a defect for a substrate, control the device    manufacturing process, monitor the device manufacturing process,    design an aspect of the device manufacturing process, and/or    calibrate a mathematical model.-   40. The method of embodiment 32, further comprising altering a    sampling of metrology data based on the distribution of alignment    data.-   41. The method of embodiment 32, further comprising using a higher    order alignment model with the distribution of alignment data    compared to that used with only the measured alignment data.-   42. The method of embodiment 32, further comprising determining the    first distribution and/or the second distribution using data    provided by a lithographic apparatus used in the device    manufacturing process.-   43. The method of embodiment 32, wherein the first distribution, the    second distribution and/or the distribution of the parameter of    interest comprises a spatial substrate fingerprint.-   44. The method of embodiment 32, wherein the device manufacturing    process comprises a lithographic process and/or a semiconductor    manufacturing process.-   45. The method of embodiment 32, wherein the function comprises one    or more selected from: an arithmetic addition, a convolution and/or    a neural network.-   46. A method comprising:

obtaining an alignment data distribution across at least part of asubstrate processed using a patterning process, based on measuredalignment data; and

combining, by a hardware computer, the alignment data distribution withan alignment fingerprint attributable to a processing parameter otherthan measured alignment to obtain an estimate of alignment data for thesubstrate.

-   47. The method of embodiment 46, wherein the alignment fingerprint    comprises a contribution of a substrate height or unflatness of the    substrate to alignment.-   48. The method of embodiment 46, wherein the alignment fingerprint    comprises a contribution of a process effect, due to a part of the    patterning process other than a lithography pattern transfer, of the    substrate to alignment.-   49. The method of embodiment 46, wherein the alignment fingerprint    comprises a contribution of heating of the substrate to alignment.-   50. The method of embodiment 46, wherein the alignment fingerprint    is specific to the patterning process but not specific to any    particular substrate processed using the patterning process.-   51. The method of embodiment 46, wherein the alignment fingerprint    is specific to a particular substrate processed using the patterning    process but not generic to other substrates processed using the    patterning process.-   52. The method of embodiment 46, wherein the alignment fingerprint    is derived from a measurement of the processing parameter.-   53. The method of embodiment 46, wherein the alignment fingerprint    comprises a spatial substrate fingerprint.-   54. The method of embodiment 46, further comprising using the    estimate to perform any one or more selected from: predict a defect    for the substrate, control the patterning process, monitor the    patterning process, design an aspect of the patterning process,    and/or calibrate a mathematical model.-   55. A computer program product comprising a non-transitory computer    readable medium having instructions recorded thereon, the    instructions when executed by a computer implementing the method of    any of embodiments 1-54.

Embodiments of the disclosure may be implemented in hardware, firmware,software, or any combination thereof. Embodiments of the disclosure mayalso be implemented as instructions stored on a machine-readable medium,which may be read and executed by one or more processors. Amachine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputing device). For example, a machine-readable medium may includeread only memory (ROM); random access memory (RAM); magnetic diskstorage media; optical storage media; flash memory devices; electrical,optical, acoustical or other forms of propagated signals (e.g. carrierwaves, infrared signals, digital signals, etc.), and others. Further,firmware, software, routines, instructions may be described herein asperforming certain actions. However, it should be appreciated that suchdescriptions are merely for convenience and that such actions in factresult from computing devices, processors, controllers, or other devicesexecuting the firmware, software, routines, instructions, etc.

In block diagrams, illustrated components are depicted as discretefunctional blocks, but embodiments are not limited to systems in whichthe functionality described herein is organized as illustrated. Thefunctionality provided by each of the components may be provided bysoftware or hardware modules that are differently organized than ispresently depicted, for example such software or hardware may beintermingled, conjoined, replicated, broken up, distributed (e.g. withina data center or geographically), or otherwise differently organized.The functionality described herein may be provided by one or moreprocessors of one or more computers executing code stored on a tangible,non-transitory, machine readable medium. In some cases, third partycontent delivery networks may host some or all of the informationconveyed over networks, in which case, to the extent information (e.g.,content) is said to be supplied or otherwise provided, the informationmay be provided by sending instructions to retrieve that informationfrom a content delivery network.

Unless specifically stated otherwise, as apparent from the discussion,it is appreciated that throughout this specification discussionsutilizing terms such as “processing,” “computing,” “calculating,”“determining” or the like refer to actions or processes of a specificapparatus, such as a special purpose computer or a similar specialpurpose electronic processing/computing device.

The reader should appreciate that the present application describesseveral inventions. Rather than separating those inventions intomultiple isolated patent applications, applicants have grouped theseinventions into a single document because their related subject matterlends itself to economies in the application process. But the distinctadvantages and aspects of such inventions should not be conflated. Insome cases, embodiments address all of the deficiencies noted herein,but it should be understood that the inventions are independentlyuseful, and some embodiments address only a subset of such problems oroffer other, unmentioned benefits that will be apparent to those ofskill in the art reviewing the present disclosure. Due to costsconstraints, some inventions disclosed herein may not be presentlyclaimed and may be claimed in later filings, such as continuationapplications or by amending the present claims. Similarly, due to spaceconstraints, neither the Abstract nor the Summary sections of thepresent document should be taken as containing a comprehensive listingof all such inventions or all aspects of such inventions.

It should be understood that the description and the drawings are notintended to limit the invention to the particular form disclosed, but tothe contrary, the intention is to cover all modifications, equivalents,and alternatives falling within the spirit and scope of the presentinvention as defined by the appended claims.

Modifications and alternative embodiments of various aspects of theinvention will be apparent to those skilled in the art in view of thisdescription. Accordingly, this description and the drawings are to beconstrued as illustrative only and are for the purpose of teaching thoseskilled in the art the general manner of carrying out the invention. Itis to be understood that the forms of the invention shown and describedherein are to be taken as examples of embodiments. Elements andmaterials may be substituted for those illustrated and described herein,parts and processes may be reversed, change in order or omitted, certainfeatures may be utilized independently, and embodiments or features ofembodiments may be combined, all as would be apparent to one skilled inthe art after having the benefit of this description of the invention.Changes may be made in the elements described herein without departingfrom the spirit and scope of the invention as described in the followingclaims. Headings used herein are for organizational purposes only andare not meant to be used to limit the scope of the description.

As used throughout this application, the word “may” is used in apermissive sense (i.e., meaning having the potential to), rather thanthe mandatory sense (i.e., meaning must). The words “include”,“including”, and “includes” and the like mean including, but not limitedto. As used throughout this application, the singular forms “a,” “an,”and “the” include plural referents unless the content explicitlyindicates otherwise. Thus, for example, reference to “an” element or “a”element includes a combination of two or more elements, notwithstandinguse of other terms and phrases for one or more elements, such as “one ormore.” The term “or” is, unless indicated otherwise, non-exclusive,i.e., encompassing both “and” and “or.” Terms describing conditionalrelationships, e.g., “in response to X, Y,” “upon X, Y,”, “if X, Y,”“when X, Y,” and the like, encompass causal relationships in which theantecedent is a necessary causal condition, the antecedent is asufficient causal condition, or the antecedent is a contributory causalcondition of the consequent, e.g., “state X occurs upon condition Yobtaining” is generic to “X occurs solely upon Y” and “X occurs upon Yand Z.” Such conditional relationships are not limited to consequencesthat instantly follow the antecedent obtaining, as some consequences maybe delayed, and in conditional statements, antecedents are connected totheir consequents, e.g., the antecedent is relevant to the likelihood ofthe consequent occurring. Statements in which a plurality of attributesor functions are mapped to a plurality of objects (e.g., one or moreprocessors performing steps A, B, C, and D) encompasses both all suchattributes or functions being mapped to all such objects and subsets ofthe attributes or functions being mapped to subsets of the attributes orfunctions (e.g., both all processors each performing steps A-D, and acase in which processor 1 performs step A, processor 2 performs step Band part of step C, and processor 3 performs part of step C and step D),unless otherwise indicated. Further, unless otherwise indicated,statements that one value or action is “based on” another condition orvalue encompass both instances in which the condition or value is thesole factor and instances in which the condition or value is one factoramong a plurality of factors. Unless otherwise indicated, statementsthat “each” instance of some collection have some property should not beread to exclude cases where some otherwise identical or similar membersof a larger collection do not have the property, i.e., each does notnecessarily mean each and every.

To the extent certain U.S. patents, U.S. patent applications, or othermaterials (e.g., articles) have been incorporated by reference, the textof such U.S. patents, U.S. patent applications, and other materials isonly incorporated by reference to the extent that no conflict existsbetween such material and the statements and drawings set forth herein.In the event of such conflict, any such conflicting text in suchincorporated by reference U.S. patents, U.S. patent applications, andother materials is specifically not incorporated by reference herein.

While specific embodiments of the disclosure have been described above,it will be appreciated that the embodiments may be practiced otherwisethan as described.

1.-20. (canceled)
 21. A method comprising: obtaining an underlyingcontribution of a lithographic apparatus to overlay as part of apatterning process; and combining, by a hardware computer, theunderlying contribution with a further contribution to overlay of asubstrate to obtain an estimate of overlay for the substrate.
 22. Themethod of claim 21, wherein the further contribution comprises acontribution of a substrate surface height of the substrate to overlay.23. The method of claim 21, wherein the further contribution comprises acontribution of a substrate servo error of the substrate to overlay. 24.The method of claim 21, wherein the further contribution comprises acontribution of an alignment and/or projection system model residual.25. The method of claim 21, further comprising combining, with theunderlying contribution and the contribution of the substrate surfaceheight, a contribution of an etch process to overlay of the substrate.26. The method of claim 25, wherein the etch process contribution isspecific to the patterning process but not specific to any particularsubstrate processed using the patterning process.
 27. The method ofclaim 21, wherein the underlying contribution is specific to aparticular patterning process but not specific to any particularsubstrate processed using the patterning process.
 28. The method ofclaim 21, wherein the obtaining the underlying contribution furthercomprises obtaining measured overlay data and removing therefrom acontribution of a particular component of the lithographic apparatus tooverlay.
 29. The method of claim 28, wherein the contribution of theparticular component comprises one or more selected from: a contributionof a servo error, a contribution of alignment model residual, acontribution of a projection system aberration, a contribution of aprojection system model residual, and/or a contribution of a substratesurface height.
 30. The method of claim 21, wherein the contributioncomprises a spatial substrate fingerprint.
 31. The method of claim 21,further comprising using the estimate to perform any one or moreselected from: predict a defect for the substrate, control thepatterning process, monitor the patterning process, design an aspect ofthe patterning process, and/or calibrate a mathematical model.
 32. Acomputer program product comprising a non-transitory computer readablemedium having instructions therein, the instructions, when executed by acomputer system, configured to cause the computer system to perform themethod of claim
 21. 33. A method comprising: obtaining an alignment datadistribution across at least part of a substrate processed using apatterning process, based on measured alignment data; and combining, bya hardware computer, the alignment data distribution with an alignmentfingerprint attributable to a processing parameter other than measuredalignment to obtain an estimate of alignment data for the substrate. 34.The method of claim 33, wherein the alignment fingerprint comprises acontribution of a substrate height or unflatness of the substrate toalignment.
 35. The method of claim 33, wherein the alignment fingerprintcomprises a contribution of a process effect, due to a part of thepatterning process other than a lithography pattern transfer, of thesubstrate to alignment.
 36. The method of claim 33, wherein thealignment fingerprint comprises a contribution of heating of thesubstrate to alignment.
 37. The method of claim 33, wherein thealignment fingerprint is specific to the patterning process but notspecific to any particular substrate processed using the patterningprocess.
 38. The method of claim 33, wherein the alignment fingerprintis specific to a particular substrate processed using the patterningprocess but not generic to other substrates processed using thepatterning process.
 39. The method of claim 33, wherein the alignmentfingerprint is derived from a measurement of the processing parameter.40. The method of claim 33, wherein the alignment fingerprint comprisesa spatial substrate fingerprint.
 41. The method of claim 33, furthercomprising using the estimate to perform any one or more selected from:predict a defect for the substrate, control the patterning process,monitor the patterning process, design an aspect of the patterningprocess, and/or calibrate a mathematical model.
 42. A computer programproduct comprising a non-transitory computer readable medium havinginstructions therein, the instructions, when executed by a computersystem, configured to cause the computer system to perform the method ofclaim 33.